Nome (mathematics)

In mathematics, specifically the theory of elliptic functions, the nome is a special function that belongs to the non-elementary functions. This function is of great importance in the description of the elliptic functions, especially in the description of the modular identity of the Jacobi theta function, the Hermite elliptic transcendents and the Weber modular functions, that are used for solving equations of higher degrees.

The nome function is given by

${\displaystyle q=\mathrm {e} ^{-{\pi K'/K}}=\mathrm {e} ^{{\rm {i}}\pi \omega _{2}/\omega _{1}}=\mathrm {e} ^{{\rm {i}}\pi \tau }\,}$

where ${\displaystyle K}$ and ${\displaystyle iK'}$ are the quarter periods, and ${\displaystyle \omega _{1}}$ and ${\displaystyle \omega _{2}}$ are the fundamental pair of periods, and ${\textstyle \tau ={\frac {iK'}{K}}={\frac {\omega _{2}}{\omega _{1}}}}$ is the half-period ratio. The nome can be taken to be a function of any one of these quantities; conversely, any one of these quantities can be taken as functions of the nome. Each of them uniquely determines the others when ${\displaystyle 0<q<1}$. That is, when ${\displaystyle 0<q<1}$, the mappings between these various symbols are both 1-to-1 and onto, and so can be inverted: the quarter periods, the half-periods and the half-period ratio can be explicitly written as functions of the nome. For general ${\displaystyle q\in \mathbb {C} }$ with ${\displaystyle 0<|q|<1}$, ${\displaystyle \tau }$ is not a single-valued function of ${\displaystyle q}$. Explicit expressions for the quarter periods, in terms of the nome, are given in the linked article.

Notationally, the quarter periods ${\displaystyle K}$ and ${\displaystyle iK'}$ are usually used only in the context of the Jacobian elliptic functions, whereas the half-periods ${\displaystyle \omega _{1}}$ and ${\displaystyle \omega _{2}}$ are usually used only in the context of Weierstrass elliptic functions. Some authors, notably Apostol, use ${\displaystyle \omega _{1}}$ and ${\displaystyle \omega _{2}}$ to denote whole periods rather than half-periods.

The nome is frequently used as a value with which elliptic functions and modular forms can be described; on the other hand, it can also be thought of as function, because the quarter periods are functions of the elliptic modulus ${\displaystyle k}$: ${\displaystyle q(k)=\mathrm {e} ^{-\pi K'(k)/K(k)}}$.

The complementary nome ${\displaystyle q_{1}}$ is given by

${\displaystyle q_{1}(k)=\mathrm {e} ^{-\pi K(k)/K'(k)}.\,}$

Sometimes the notation ${\displaystyle q=\mathrm {e} ^{{2{\rm {i}}}\pi \tau }}$ is used for the square of the nome.

The mentioned functions ${\displaystyle K}$ and ${\displaystyle K'}$ are called complete elliptic integrals of the first kind. They are defined as follows:

${\displaystyle K(x)=\int _{0}^{\pi /2}{\frac {1}{\sqrt {1-x^{2}\sin(\varphi )^{2}}}}\,\mathrm {d} \varphi =\int _{0}^{1}{\frac {2}{\sqrt {(y^{2}+1)^{2}-4x^{2}y^{2}}}}\mathrm {d} y}$

${\displaystyle K'(x)=K({\sqrt {1-x^{2}}})=\int _{0}^{\pi /2}{\frac {1}{\sqrt {1-(1-x^{2})\sin(\varphi )^{2}}}}\,\mathrm {d} \varphi }$

The nome solves the following equation:

${\displaystyle |k|={\frac {\vartheta _{10}^{2}[0,q(k)]}{\vartheta _{00}^{2}[0,q(k)]}}\rightarrow q(k)=\mathrm {e} ^{-\pi K'(k)/K(k)}}$

This analogon is valid for the Pythagorean complementary modulus:

${\displaystyle k'={\sqrt {1-k^{2}}}={\frac {\vartheta _{01}^{2}[0,q(k)]}{\vartheta _{00}^{2}[0,q(k)]}}\rightarrow q(k)=\mathrm {e} ^{-\pi K'(k)/K(k)}}$

where ${\displaystyle \vartheta _{10},\theta _{00}}$ are the complete Jacobi theta functions and ${\displaystyle K(k)}$ is the complete elliptic integral of the first kind with modulus ${\displaystyle k}$ shown in the formula above. For the complete theta functions these definitions introduced by Sir Edmund Taylor Whittaker and George Neville Watson are valid:

${\displaystyle \vartheta _{00}(v;w)=\prod _{n=1}^{\infty }(1-w^{2n})[1+2\cos(2v)w^{2n-1}+w^{4n-2}]}$

${\displaystyle \vartheta _{01}(v;w)=\prod _{n=1}^{\infty }(1-w^{2n})[1-2\cos(2v)w^{2n-1}+w^{4n-2}]}$

${\displaystyle \vartheta _{10}(v;w)=2w^{1/4}\cos(v)\prod _{n=1}^{\infty }(1-w^{2n})[1+2\cos(2v)w^{2n}+w^{4n}]}$

These three definition formulas are written down in the fourth edition of the book A Course in Modern Analysis written by Whittaker and Watson on the pages 469 and 470. The nome is commonly used as the starting point for the construction of Lambert series, the q-series and more generally the q-analogs. That is, the half-period ratio ${\displaystyle \tau }$ is commonly used as a coordinate on the complex upper half-plane, typically endowed with the Poincaré metric to obtain the Poincaré half-plane model. The nome then serves as a coordinate on a punctured disk of unit radius; it is punctured because ${\displaystyle q=0}$ is not part of the disk (or rather, ${\displaystyle q=0}$ corresponds to ${\displaystyle \tau \to \infty }$). This endows the punctured disk with the Poincaré metric.

The upper half-plane (and the Poincaré disk, and the punctured disk) can thus be tiled with the fundamental domain, which is the region of values of the half-period ratio ${\displaystyle \tau }$ (or of ${\displaystyle q}$, or of ${\displaystyle K}$ and ${\displaystyle iK'}$ etc.) that uniquely determine a tiling of the plane by parallelograms. The tiling is referred to as the modular symmetry given by the modular group. Some functions that are periodic on the upper half-plane are called to as modular functions; the nome, the half-periods, the quarter-periods or the half-period ratio all provide different parameterizations for these periodic functions.

The prototypical modular function is Klein's j-invariant. It can be written as a function of either the half-period ratio τ or as a function of the nome ${\displaystyle q}$. The series expansion in terms of the nome or the square of the nome (the q-expansion) is famously connected to the Fisher-Griess monster by means of monstrous moonshine.

Euler's function arises as the prototype for q-series in general.

The nome, as the ${\displaystyle q}$ of q-series then arises in the theory of affine Lie algebras, essentially because (to put it poetically, but not factually)^{[citation needed]} those algebras describe the symmetries and isometries of Riemann surfaces.

Every real value ${\displaystyle x}$ of the interval ${\displaystyle [-1,1]}$ is assigned to a real number between inclusive zero and inclusive one in the nome function ${\displaystyle q(x)}$. The elliptic nome function is axial symmetric to the ordinate axis. Thus: ${\displaystyle q(x)=q(-x)}$. The functional curve of the nome passes through the origin of coordinates with the slope zero and curvature plus one eighth. For the real valued interval ${\displaystyle (-1,1)}$ the nome function ${\displaystyle q(x)}$ is strictly left-curved.

The Legendre's relation is defined that way:

${\displaystyle K\,E'+E\,K'-K\,K'={\tfrac {1}{2}}\pi }$

And as described above, the elliptic nome function ${\displaystyle q(x)}$ has this original definition:

${\displaystyle q(x)=\exp \left[-\pi \,{\frac {K({\sqrt {1-x^{2}}})}{K(x)}}\right]}$

Furthermore, these are the derivatives of the two complete elliptic integrals:

${\displaystyle {\frac {\mathrm {d} }{\mathrm {d} x}}K(x)={\frac {1}{x(1-x^{2})}}{\bigl [}E(x)-(1-x^{2})K(x){\bigr ]}}$

${\displaystyle {\frac {\mathrm {d} }{\mathrm {d} x}}E(x)=-{\frac {1}{x}}{\bigl [}K(x)-E(x){\bigr ]}}$

Therefore, the derivative of the nome function has the following expression:

${\displaystyle {\frac {\mathrm {d} }{\mathrm {d} x}}\,q(x)={\frac {\pi ^{2}}{2x(1-x^{2})K(x)^{2}}}\,q(x)}$

The second derivative can be expressed this way:

${\displaystyle {\frac {\mathrm {d} ^{2}}{\mathrm {d} x^{2}}}\,q(x)={\frac {\pi ^{4}+2\pi ^{2}(1+x^{2})K(x)^{2}-4\pi ^{2}K(x)E(x)}{4x^{2}(1-x^{2})^{2}K(x)^{4}}}\,q(x)}$

And that is the third derivative:

${\displaystyle {\frac {\mathrm {d} ^{3}}{\mathrm {d} x^{3}}}\,q(x)={\frac {\pi ^{6}+6\pi ^{4}(1+x^{2})K(x)^{2}-12\pi ^{4}K(x)E(x)+8\pi ^{2}(1+x^{2})^{2}K(x)^{4}-24\pi ^{2}(1+x^{2})K(x)^{3}E(x)+24\pi ^{2}K(x)^{2}E(x)^{2}}{8x^{3}(1-x^{2})^{3}K(x)^{6}}}\,q(x)}$

The complete elliptic integral of the second kind is defined as follows:

${\displaystyle E(x)=\int _{0}^{\pi /2}{\sqrt {1-x^{2}\sin(\varphi )^{2}}}\,\mathrm {d} \varphi =2\int _{0}^{1}{\frac {\sqrt {(y^{2}+1)^{2}-4x^{2}y^{2}}}{(y^{2}+1)^{2}}}\,\mathrm {d} y}$

The following equation follows from these equations by eliminating the complete elliptic integral of the second kind:

${\displaystyle 3{\biggl [}{\frac {\mathrm {d} ^{2}}{\mathrm {d} x^{2}}}q(x){\biggr ]}^{2}-2{\biggl [}{\frac {\mathrm {d} }{\mathrm {d} x}}q(x){\biggr ]}{\biggl [}{\frac {\mathrm {d} ^{3}}{\mathrm {d} x^{3}}}q(x){\biggr ]}={\frac {\pi ^{8}-4\pi ^{4}(1+x^{2})^{2}K(x)^{4}}{16x^{4}(1-x^{2})^{4}K(x)^{8}}}q(x)^{2}}$

Thus, the following third-order quartic differential equation is valid:

${\displaystyle x^{2}(1-x^{2})^{2}[2q(x)^{2}q'(x)q'''(x)-3q(x)^{2}q''(x)^{2}+q'(x)^{4}]=(1+x^{2})^{2}q(x)^{2}q'(x)^{2}}$

Given is the derivative of the Elliptic Nome mentioned above:

${\displaystyle {\frac {\mathrm {d} }{\mathrm {d} x}}\,q(x)={\frac {\pi ^{2}}{2x(1-x^{2})K(x)^{2}}}\,q(x)}$

The outer factor with the K-integral in the denominator shown in this equation is the derivative of the elliptic period ratio. The elliptic period ratio is the quotient of the K-integral of the Pythagorean complementary modulus divided by the K-integral of the modulus itself. And the integer number sequence in MacLaurin series of that elliptic period ratio leads to the integer sequence of the series of the elliptic nome directly.

The German mathematician Adolf Kneser researched on the integer sequence of the elliptic period ratio in his essay Neue Untersuchung einer Reihe aus der Theorie der elliptischen Funktionen and showed that the generating function of this sequence is an elliptic function. Also a further mathematician with the name Robert Fricke analyzed this integer sequence in his essay Die elliptischen Funktionen und ihre Anwendungen and described the accurate computing methods by using this mentioned sequence. The Kneser integer sequence Kn(n) can be constructed in this way:

${\displaystyle {\text{Kn}}(2n)=2^{4n-3}{\binom {4n}{2n}}+\sum _{m=1}^{n}4^{2n-2m}{\binom {4n}{2n-2m}}{\text{Kn}}(m)}$

${\displaystyle {\text{Kn}}(2n+1)=2^{4n-1}{\binom {4n+2}{2n+1}}+\sum _{m=1}^{n}4^{2n-2m+1}{\binom {4n+2}{2n-2m+1}}{\text{Kn}}(m)}$

Executed examples:

${\displaystyle {\text{Kn}}(2)=2\times 6+1\times {\color {cornflowerblue}1}={\color {cornflowerblue}13}}$

${\displaystyle {\text{Kn}}(3)=8\times 20+24\times {\color {cornflowerblue}1}={\color {cornflowerblue}184}}$

${\displaystyle {\text{Kn}}(4)=32\times 70+448\times {\color {cornflowerblue}1}+1\times {\color {cornflowerblue}13}={\color {cornflowerblue}2701}}$

${\displaystyle {\text{Kn}}(5)=128\times 252+7680\times {\color {cornflowerblue}1}+40\times {\color {cornflowerblue}13}={\color {cornflowerblue}40456}}$

${\displaystyle {\text{Kn}}(6)=512\times 924+126720\times {\color {cornflowerblue}1}+1056\times {\color {cornflowerblue}13}+1\times {\color {cornflowerblue}184}={\color {cornflowerblue}613720}}$

${\displaystyle {\text{Kn}}(7)=2048\times 3432+2050048\times {\color {cornflowerblue}1}+23296\times {\color {cornflowerblue}13}+56\times {\color {cornflowerblue}184}={\color {cornflowerblue}9391936}}$

The Kneser sequence appears in the Taylor series of the period ratio (half period ratio):

${\displaystyle {\frac {1}{4}}\ln {\bigl (}{\frac {16}{x^{2}}}{\bigr )}-{\frac {\pi \,K'(x)}{4\,K(x)}}=\sum _{n=1}^{\infty }{\frac {{\text{Kn}}(n)}{2^{4n-1}n}}\,x^{2n}}$

${\displaystyle {\color {limegreen}{\frac {1}{4}}\ln {\bigl (}{\frac {16}{x^{2}}}{\bigr )}-{\frac {\pi \,K'(x)}{4\,K(x)}}={\frac {\color {cornflowerblue}1}{8}}x^{2}+{\frac {\color {cornflowerblue}13}{256}}x^{4}+{\frac {\color {cornflowerblue}184}{6144}}x^{6}+{\frac {\color {cornflowerblue}2701}{131072}}x^{8}+{\frac {\color {cornflowerblue}40456}{2621440}}x^{10}+\ldots }}$

The derivative of this equation after ${\displaystyle x}$ leads to this equation that shows the generating function of the Kneser number sequence:

${\displaystyle {\frac {\pi ^{2}}{8x(1-x^{2})K(x)^{2}}}-{\frac {1}{2x}}=\sum _{n=1}^{\infty }{\frac {{\text{Kn}}(n)}{2^{4n-2}}}x^{2n-1}}$

${\displaystyle {\color {limegreen}{\frac {\pi ^{2}}{8x(1-x^{2})K(x)^{2}}}-{\frac {1}{2x}}={\frac {\color {cornflowerblue}1}{4}}x+{\frac {\color {cornflowerblue}13}{64}}x^{3}+{\frac {\color {cornflowerblue}184}{1024}}x^{5}+{\frac {\color {cornflowerblue}2701}{16384}}x^{7}+{\frac {\color {cornflowerblue}40456}{262144}}x^{9}+\ldots }}$

This result appears because of the Legendre's relation ${\displaystyle K\,E'+E\,K'-K\,K'={\tfrac {1}{2}}\pi }$ in the numerator.

The mathematician Karl Heinrich Schellbach [de] discovered the integer number sequence that appears in the MacLaurin series of the fourth root of the quotient Elliptic Nome function divided by the square function. The construction of this sequence is detailed in his work Die Lehre von den Elliptischen Integralen und den Thetafunktionen.^[1]: 60 The sequence was also constructed by the Silesian German mathematician Hermann Amandus Schwarz in Formeln und Lehrsätze zum Gebrauche der elliptischen Funktionen^[2] (pages 54–56, chapter Berechnung der Grösse k). This Schellbach Schwarz number sequence Sc(n) was also analyzed by the mathematicians Karl Theodor Wilhelm Weierstrass and Louis Melville Milne-Thomson in the 20th century. The mathematician Adolf Kneser determined a construction for this sequence based on the following pattern:

${\displaystyle {\text{Sc}}(n+1)={\frac {2}{n}}\sum _{m=1}^{n}{\text{Sc}}(m)\,{\text{Kn}}(n+1-m)}$

The Schellbach Schwarz sequence Sc(n) appears in the On-Line Encyclopedia of Integer Sequences under the number A002103 and the Kneser sequence Kn(n) appears under the number A227503.

The following table^[3][4] contains the Kneser numbers and the Schellbach Schwarz numbers:

And this sequence creates the MacLaurin series of the elliptic nome^[5][6][7] in exactly this way:

${\displaystyle q(x)=\sum _{n=1}^{\infty }{\frac {{\text{Sc}}(n)}{2^{4n-3}}}{\biggl (}{\frac {1-{\sqrt[{4}]{1-x^{2}}}}{1+{\sqrt[{4}]{1-x^{2}}}}}{\biggr )}^{4n-3}=x^{2}{\biggl \{}{\frac {1}{2}}+{\biggl [}\sum _{n=1}^{\infty }{\frac {{\text{Sc}}(n+1)}{2^{4n+1}}}x^{2n}{\biggr ]}{\biggr \}}^{4}}$

${\displaystyle q(x)=x^{2}{\bigl (}{\color {limegreen}{\frac {\color {navy}1}{2}}+{\frac {\color {navy}2}{32}}x^{2}+{\frac {\color {navy}15}{512}}x^{4}+{\frac {\color {navy}150}{8192}}x^{6}+{\frac {\color {navy}1707}{131072}}x^{8}+\ldots }{\bigr )}^{4}}$

In the following, it will be shown as an example how the Schellbach Schwarz numbers are built up successively. For this, the examples with the numbers Sc(4) = 150, Sc(5) = 1707 and Sc(6) = 20910 are used:

${\displaystyle \mathrm {Sc} (4)={\frac {2}{3}}\sum _{m=1}^{3}\mathrm {Sc} (m)\,\mathrm {Kn} (4-m)={\frac {2}{3}}{\bigl [}{\color {navy}\mathrm {Sc} (1)}\,{\color {cornflowerblue}\mathrm {Kn} (3)}+{\color {navy}\mathrm {Sc} (2)}\,{\color {cornflowerblue}\mathrm {Kn} (2)}+{\color {navy}\mathrm {Sc} (3)}\,{\color {cornflowerblue}\mathrm {Kn} (1)}{\bigr ]}}$

${\displaystyle {\color {navy}\mathrm {Sc} (4)}={\frac {2}{3}}{\bigl (}{\color {navy}1}\times {\color {cornflowerblue}184}+{\color {navy}2}\times {\color {cornflowerblue}13}+{\color {navy}15}\times {\color {cornflowerblue}1}{\bigr )}={\color {navy}150}}$

${\displaystyle \mathrm {Sc} (5)={\frac {2}{4}}\sum _{m=1}^{4}\mathrm {Sc} (m)\,\mathrm {Kn} (5-m)={\frac {2}{4}}{\bigl [}{\color {navy}\mathrm {Sc} (1)}\,{\color {cornflowerblue}\mathrm {Kn} (4)}+{\color {navy}\mathrm {Sc} (2)}\,{\color {cornflowerblue}\mathrm {Kn} (3)}+{\color {navy}\mathrm {Sc} (3)}\,{\color {cornflowerblue}\mathrm {Kn} (2)}+{\color {navy}\mathrm {Sc} (4)}\,{\color {cornflowerblue}\mathrm {Kn} (1)}{\bigr ]}}$

${\displaystyle {\color {navy}\mathrm {Sc} (5)}={\frac {2}{4}}{\bigl (}{\color {navy}1}\times {\color {cornflowerblue}2701}+{\color {navy}2}\times {\color {cornflowerblue}184}+{\color {navy}15}\times {\color {cornflowerblue}13}+{\color {navy}150}\times {\color {cornflowerblue}1}{\bigr )}={\color {navy}1707}}$

${\displaystyle \mathrm {Sc} (6)={\frac {2}{5}}\sum _{m=1}^{5}\mathrm {Sc} (m)\,\mathrm {Kn} (6-m)={\frac {2}{5}}{\bigl [}{\color {navy}\mathrm {Sc} (1)}\,{\color {cornflowerblue}\mathrm {Kn} (5)}+{\color {navy}\mathrm {Sc} (2)}\,{\color {cornflowerblue}\mathrm {Kn} (4)}+{\color {navy}\mathrm {Sc} (3)}\,{\color {cornflowerblue}\mathrm {Kn} (3)}+{\color {navy}\mathrm {Sc} (4)}\,{\color {cornflowerblue}\mathrm {Kn} (2)}+{\color {navy}\mathrm {Sc} (5)}\,{\color {cornflowerblue}\mathrm {Kn} (1)}{\bigr ]}}$

${\displaystyle {\color {navy}\mathrm {Sc} (6)}={\frac {2}{5}}{\bigl (}{\color {navy}1}\times {\color {cornflowerblue}40456}+{\color {navy}2}\times {\color {cornflowerblue}2701}+{\color {navy}15}\times {\color {cornflowerblue}184}+{\color {navy}150}\times {\color {cornflowerblue}13}+{\color {navy}1707}\times {\color {cornflowerblue}1}{\bigr )}={\color {navy}20910}}$

The MacLaurin series of the nome function ${\displaystyle q(x)}$ has even exponents and positive coefficients at all positions:

${\displaystyle q(x)=\sum _{n=1}^{\infty }{\frac {\operatorname {Kt} (n)}{16^{n}}}\,x^{2n}}$

And the sum with the same absolute values of the coefficients but with alternating signs generates this function:

${\displaystyle q{\bigl [}x(x^{2}+1)^{-1/2}{\bigr ]}=\sum _{n=1}^{\infty }{\frac {(-1)^{n+1}\operatorname {Kt} (n)}{16^{n}}}\,x^{2n}}$

The radius of convergence of this Maclaurin series is 1. Here ${\displaystyle \operatorname {Kt} (n)}$ (OEIS A005797) is a sequence of exclusively natural numbers ${\displaystyle \operatorname {Kt} (n)\in \mathbb {N} }$ for all natural numbers ${\displaystyle n\in \mathbb {N} }$ and this integer number sequence is not elementary. This sequence of numbers ${\displaystyle \operatorname {Kt} (n)}$ was researched by the Czech mathematician and fairy chess composer Václav Kotěšovec, born in 1956. Two ways of constructing this integer sequence shall be shown in the next section.

The Kotěšovec numbers are generated in the same way as the Schellbach Schwarz numbers are constructed:

The only difference consists in the fact that this time the factor before the sum in this corresponding analogous formula is not ${\displaystyle {\frac {2}{n}}}$ anymore, but ${\displaystyle {\frac {8}{n}}}$ instead of that:

${\displaystyle {\text{Kt}}(n+1)={\frac {8}{n}}\sum _{m=1}^{n}{\text{Kt}}(m)\,{\text{Kn}}(n+1-m)}$

Following table contains the Schellbach Schwarz numbers and the Kneser numbers and the Apéry numbers:

In the following, it will be shown as an example how the Schellbach Schwarz numbers are built up successively. For this, the examples with the numbers Kt(4) = 992, Kt(5) = 12514 and Kt(6) = 164688 are used:

${\displaystyle \mathrm {Kt} (4)={\frac {8}{3}}\sum _{m=1}^{3}\mathrm {Kt} (m)\,\mathrm {Kn} (4-m)={\frac {8}{3}}{\bigl [}{\color {ForestGreen}\mathrm {Kt} (1)}\,{\color {cornflowerblue}\mathrm {Kn} (3)}+{\color {ForestGreen}\mathrm {Kt} (2)}\,{\color {cornflowerblue}\mathrm {Kn} (2)}+{\color {ForestGreen}\mathrm {Kt} (3)}\,{\color {cornflowerblue}\mathrm {Kn} (1)}{\bigr ]}}$

${\displaystyle {\color {ForestGreen}\mathrm {Kt} (4)}={\frac {8}{3}}{\bigl (}{\color {ForestGreen}1}\times {\color {cornflowerblue}184}+{\color {ForestGreen}8}\times {\color {cornflowerblue}13}+{\color {ForestGreen}84}\times {\color {cornflowerblue}1}{\bigr )}={\color {ForestGreen}992}}$

${\displaystyle \mathrm {Kt} (5)={\frac {8}{4}}\sum _{m=1}^{4}\mathrm {Kt} (m)\,\mathrm {Kn} (5-m)={\frac {8}{4}}{\bigl [}{\color {ForestGreen}\mathrm {Kt} (1)}\,{\color {cornflowerblue}\mathrm {Kn} (4)}+{\color {ForestGreen}\mathrm {Kt} (2)}\,{\color {cornflowerblue}\mathrm {Kn} (3)}+{\color {ForestGreen}\mathrm {Kt} (3)}\,{\color {cornflowerblue}\mathrm {Kn} (2)}+{\color {ForestGreen}\mathrm {Kt} (4)}\,{\color {cornflowerblue}\mathrm {Kn} (1)}{\bigr ]}}$

${\displaystyle {\color {ForestGreen}\mathrm {Kt} (5)}={\frac {8}{4}}{\bigl (}{\color {ForestGreen}1}\times {\color {cornflowerblue}2701}+{\color {ForestGreen}8}\times {\color {cornflowerblue}184}+{\color {ForestGreen}84}\times {\color {cornflowerblue}13}+{\color {ForestGreen}992}\times {\color {cornflowerblue}1}{\bigr )}={\color {ForestGreen}12514}}$

${\displaystyle \mathrm {Kt} (6)={\frac {8}{5}}\sum _{m=1}^{5}\mathrm {Kt} (m)\,\mathrm {Kn} (6-m)={\frac {8}{5}}{\bigl [}{\color {ForestGreen}\mathrm {Kt} (1)}\,{\color {cornflowerblue}\mathrm {Kn} (5)}+{\color {ForestGreen}\mathrm {Kt} (2)}\,{\color {cornflowerblue}\mathrm {Kn} (4)}+{\color {ForestGreen}\mathrm {Kt} (3)}\,{\color {cornflowerblue}\mathrm {Kn} (3)}+{\color {ForestGreen}\mathrm {Kt} (4)}\,{\color {cornflowerblue}\mathrm {Kn} (2)}+{\color {ForestGreen}\mathrm {Kt} (5)}\,{\color {cornflowerblue}\mathrm {Kn} (1)}{\bigr ]}}$

${\displaystyle {\color {ForestGreen}\mathrm {Kt} (6)}={\frac {8}{5}}{\bigl (}{\color {ForestGreen}1}\times {\color {cornflowerblue}40456}+{\color {ForestGreen}8}\times {\color {cornflowerblue}2701}+{\color {ForestGreen}84}\times {\color {cornflowerblue}184}+{\color {ForestGreen}992}\times {\color {cornflowerblue}13}+{\color {ForestGreen}12514}\times {\color {cornflowerblue}1}{\bigr )}={\color {ForestGreen}164688}}$

So the MacLaurin series of the direct Elliptic Nome can be generated:

${\displaystyle q(x)=\sum _{n=1}^{\infty }{\frac {{\text{Kt}}(n)}{16^{n}}}\,x^{2n}}$

${\displaystyle q(x)={\color {limegreen}{\frac {\color {ForestGreen}1}{16}}x^{2}+{\frac {\color {ForestGreen}8}{256}}x^{4}+{\frac {\color {ForestGreen}84}{4096}}x^{6}+{\frac {\color {ForestGreen}992}{65536}}x^{8}+{\frac {\color {ForestGreen}12514}{1048576}}x^{10}+\ldots }}$

By adding a further integer number sequence ${\displaystyle \operatorname {Ap} (n)}$ that denotes a specially modified Apéry sequence (OEIS A036917), the sequence of the Kotěšovec numbers ${\displaystyle \operatorname {Kt} (n)}$ can be generated. The starting value of the sequence ${\displaystyle \operatorname {Kt} (n)}$ is the value ${\displaystyle \operatorname {Kt} (1)=1}$ and the following values of this sequence are generated with those two formulas that are valid for all numbers ${\displaystyle n\in \mathbb {N} }$:

${\displaystyle \operatorname {Kt} (n+1)={\frac {1}{n}}\sum _{m=1}^{n}m\operatorname {Kt} (m)[16\operatorname {Ap} (n+1-m)-\operatorname {Ap} (n+2-m)]}$

${\displaystyle \operatorname {Ap} (n)=\sum _{a=0}^{n-1}{\binom {2a}{a}}^{2}{\binom {2n-2-2a}{n-1-a}}^{2}}$

This formula creates the Kotěšovec sequence too, but it only creates the sequence numbers of even indices:

${\displaystyle \operatorname {Kt} (2n)={\frac {1}{2}}\sum _{m=1}^{2n-1}(-1)^{2n-m+1}16^{2n-m}{\binom {2n-1}{m-1}}\operatorname {Kt} (m)}$

The Apéry sequence ${\displaystyle \operatorname {Ap} (n)}$ was researched especially by the mathematicians Sun Zhi-Hong and Reinhard Zumkeller. And that sequence generates the square of the complete elliptic integral of the first kind:

${\displaystyle 4\pi ^{-2}K(x)^{2}=1+\sum _{n=1}^{\infty }{\frac {\operatorname {Ap} (n+1)x^{2n}}{16^{n}}}}$

The first numerical values of the central binomial coefficients and the two numerical sequences described are listed in the following table:

Index n	Central binomial coefficient square ${\displaystyle {\frac {[(2n-2)!]^{2}}{[(n-1)!]^{4}}}}$	Sequence number Ap(n)	Sequence number Kt(n)
1	1	1	1
2	4	8	8
3	36	88	84
4	400	1088	992
5	4900	14296	12514
6	63504	195008	164688
7	853776	2728384	2232200
8	11778624	38879744	30920128
9	165636900	561787864	435506703
10	2363904400	8206324928	6215660600
11	34134779536	120929313088	89668182220
12	497634306624	1794924383744	1305109502496
13	7312459672336	26802975999424	19138260194422
14	108172480360000	402298219288064	282441672732656
15	1609341595560000	6064992788397568	4191287776164504
16	24061445010950400	91786654611673088	62496081197436736
17	361297635242552100	1393772628452578264	935823746406530603

Václav Kotěšovec wrote down the number sequence ${\displaystyle \operatorname {Kt} (n)}$ on the Online Encyclopedia of Integer Sequences up to the seven hundredth sequence number.

Here one example of the Kotěšovec sequence is computed:

${\displaystyle {\color {blue}1}\times {\color {blue}63504}+{\color {blue}4}\times {\color {blue}4900}+{\color {blue}36}\times {\color {blue}400}+{\color {blue}400}\times {\color {blue}36}+{\color {blue}4900}\times {\color {blue}4}+{\color {blue}63504}\times {\color {blue}1}={\color {RoyalBlue}195008}}$ ${\displaystyle {\tfrac {1}{5}}\times {\color {ForestGreen}1}\times (16\times {\color {RoyalBlue}14296}-{\color {RoyalBlue}195008})+{\tfrac {2}{5}}\times {\color {ForestGreen}8}\times (16\times {\color {RoyalBlue}1088}-{\color {RoyalBlue}14296})+{\tfrac {3}{5}}\times {\color {ForestGreen}84}\times (16\times {\color {RoyalBlue}88}-{\color {RoyalBlue}1088})+{}}$ ${\displaystyle {}+{\tfrac {4}{5}}\times {\color {ForestGreen}992}\times (16\times {\color {RoyalBlue}8}-{\color {RoyalBlue}88})+{\tfrac {5}{5}}\times {\color {ForestGreen}12514}\times (16\times {\color {RoyalBlue}1}-{\color {RoyalBlue}8})={\color {ForestGreen}164688}}$

The two following lists contain many function values of the nome function:

The first list shows pairs of values with mutually Pythagorean complementary modules:

${\displaystyle q({\tfrac {1}{2}}{\sqrt {2}})=\exp(-\pi )}$

${\displaystyle q[{\tfrac {1}{4}}({\sqrt {6}}-{\sqrt {2}})]=\exp(-{\sqrt {3}}\,\pi )}$

${\displaystyle q[{\tfrac {1}{4}}({\sqrt {6}}+{\sqrt {2}})]=\exp(-{\tfrac {1}{3}}{\sqrt {3}}\,\pi )}$

${\displaystyle q{\bigl \{}\sin {\bigl [}{\tfrac {1}{2}}\arcsin({\sqrt {5}}-2){\bigr ]}{\bigr \}}=\exp(-{\sqrt {5}}\,\pi )}$

${\displaystyle q{\bigl \{}\cos {\bigl [}{\tfrac {1}{2}}\arcsin({\sqrt {5}}-2){\bigr ]}{\bigr \}}=\exp(-{\tfrac {1}{5}}{\sqrt {5}}\,\pi )}$

${\displaystyle q[{\tfrac {1}{8}}(3{\sqrt {2}}-{\sqrt {14}})]=\exp(-{\sqrt {7}}\,\pi )}$

${\displaystyle q[{\tfrac {1}{8}}(3{\sqrt {2}}+{\sqrt {14}})]=\exp(-{\tfrac {1}{7}}{\sqrt {7}}\,\pi )}$

${\displaystyle q[{\tfrac {1}{2}}({\sqrt {3}}-1)({\sqrt {2}}-{\sqrt[{4}]{3}})]=\exp(-3\pi )}$

${\displaystyle q[{\tfrac {1}{2}}({\sqrt {3}}-1)({\sqrt {2}}+{\sqrt[{4}]{3}})]=\exp(-{\tfrac {1}{3}}\pi )}$

${\displaystyle q{\bigl [}{\tfrac {1}{16}}{\bigl (}{\sqrt {22}}+3{\sqrt {2}}{\bigr )}{\bigl (}{\tfrac {1}{3}}{\sqrt[{3}]{6{\sqrt {3}}+2{\sqrt {11}}}}-{\tfrac {1}{3}}{\sqrt[{3}]{6{\sqrt {3}}-2{\sqrt {11}}}}+{\tfrac {1}{3}}{\sqrt {11}}-1{\bigr )}^{4}{\bigr ]}=\exp(-{\sqrt {11}}\,\pi )}$

${\displaystyle q{\bigl [}{\tfrac {1}{16}}{\bigl (}{\sqrt {22}}-3{\sqrt {2}}{\bigr )}{\bigl (}{\tfrac {1}{3}}{\sqrt[{3}]{6{\sqrt {3}}+2{\sqrt {11}}}}-{\tfrac {1}{3}}{\sqrt[{3}]{6{\sqrt {3}}-2{\sqrt {11}}}}+{\tfrac {1}{3}}{\sqrt {11}}+1{\bigr )}^{4}{\bigr ]}=\exp(-{\tfrac {1}{11}}{\sqrt {11}}\,\pi )}$

${\displaystyle q{\bigl \{}\sin {\bigl [}{\tfrac {1}{2}}\arcsin(5{\sqrt {13}}-18){\bigr ]}{\bigr \}}=\exp(-{\sqrt {13}}\,\pi )}$

${\displaystyle q{\bigl \{}\cos {\bigl [}{\tfrac {1}{2}}\arcsin(5{\sqrt {13}}-18){\bigr ]}{\bigr \}}=\exp(-{\tfrac {1}{13}}{\sqrt {13}}\,\pi )}$

The second list shows pairs of values with mutually tangentially complementary modules:

${\displaystyle q({\sqrt {2}}-1)=\exp(-{\sqrt {2}}\,\pi )}$

${\displaystyle q[(2-{\sqrt {3}})({\sqrt {3}}-{\sqrt {2}})]=\exp(-{\sqrt {6}}\,\pi )}$

${\displaystyle q[(2-{\sqrt {3}})({\sqrt {3}}+{\sqrt {2}})]=\exp(-{\tfrac {1}{3}}{\sqrt {6}}\,\pi )}$

${\displaystyle q[({\sqrt {10}}-3)({\sqrt {2}}-1)^{2}]=\exp(-{\sqrt {10}}\,\pi )}$

${\displaystyle q[({\sqrt {10}}-3)({\sqrt {2}}+1)^{2}]=\exp(-{\tfrac {1}{5}}{\sqrt {10}}\,\pi )}$

${\displaystyle q{\bigl [}{\tfrac {1}{16}}{\sqrt {2{\sqrt {2}}-{\sqrt {7}}}}\,(3{\sqrt {2}}-{\sqrt {14}})({\sqrt {2{\sqrt {2}}+1}}-1)^{4}{\bigr ]}=\exp(-{\sqrt {14}}\,\pi )}$

${\displaystyle q{\bigl [}{\tfrac {1}{16}}{\sqrt {2{\sqrt {2}}+{\sqrt {7}}}}\,(3{\sqrt {2}}+{\sqrt {14}})({\sqrt {2{\sqrt {2}}+1}}-1)^{4}{\bigr ]}=\exp(-{\tfrac {1}{7}}{\sqrt {14}}\,\pi )}$

${\displaystyle q[(2-{\sqrt {3}})^{2}({\sqrt {2}}-1)^{3}]=\exp(-3{\sqrt {2}}\,\pi )}$

${\displaystyle q[(2+{\sqrt {3}})^{2}({\sqrt {2}}-1)^{3}]=\exp(-{\tfrac {1}{3}}{\sqrt {2}}\,\pi )}$

${\displaystyle q[(10-3{\sqrt {11}})(3{\sqrt {11}}-7{\sqrt {2}})]=\exp(-{\sqrt {22}}\,\pi )}$

${\displaystyle q[(10-3{\sqrt {11}})(3{\sqrt {11}}+7{\sqrt {2}})]=\exp(-{\tfrac {1}{11}}{\sqrt {22}}\,\pi )}$

${\displaystyle q{\bigl \{}({\sqrt {26}}+5)({\sqrt {2}}-1)^{2}\tan {\bigl [}{\tfrac {1}{4}}\pi -\arctan({\tfrac {1}{3}}{\sqrt[{3}]{3{\sqrt {3}}+{\sqrt {26}}}}-{\tfrac {1}{3}}{\sqrt[{3}]{3{\sqrt {3}}-{\sqrt {26}}}}+{\tfrac {1}{6}}{\sqrt {26}}-{\tfrac {1}{2}}{\sqrt {2}}){\bigr ]}^{4}{\bigr \}}=\exp(-{\sqrt {26}}\,\pi )}$

${\displaystyle q{\bigl \{}({\sqrt {26}}+5)({\sqrt {2}}+1)^{2}\tan {\bigl [}\arctan({\tfrac {1}{3}}{\sqrt[{3}]{3{\sqrt {3}}+{\sqrt {26}}}}-{\tfrac {1}{3}}{\sqrt[{3}]{3{\sqrt {3}}-{\sqrt {26}}}}+{\tfrac {1}{6}}{\sqrt {26}}+{\tfrac {1}{2}}{\sqrt {2}})-{\tfrac {1}{4}}\pi {\bigr ]}^{4}{\bigr \}}=\exp(-{\tfrac {1}{13}}{\sqrt {26}}\,\pi )}$

Related quartets of values are shown below:

${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[({\sqrt {10}}-3)^{2}({\sqrt {5}}-2)^{2}]\}{\bigr \rangle }=\exp(-{\sqrt {30}}\,\pi )}$ ${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[({\sqrt {10}}-3)^{2}({\sqrt {5}}+2)^{2}]\}{\bigr \rangle }=\exp(-{\tfrac {1}{3}}{\sqrt {30}}\,\pi )}$ ${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[({\sqrt {10}}+3)^{2}({\sqrt {5}}-2)^{2}]\}{\bigr \rangle }=\exp(-{\tfrac {1}{5}}{\sqrt {30}}\,\pi )}$ ${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[({\sqrt {10}}+3)^{2}({\sqrt {5}}+2)^{2}]\}{\bigr \rangle }=\exp(-{\tfrac {1}{15}}{\sqrt {30}}\,\pi )}$

${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[(2{\sqrt {7}}-3{\sqrt {3}})^{2}(2{\sqrt {2}}-{\sqrt {7}})^{2}]\}{\bigr \rangle }=\exp(-{\sqrt {42}}\,\pi )}$ ${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[(2{\sqrt {7}}-3{\sqrt {3}})^{2}(2{\sqrt {2}}+{\sqrt {7}})^{2}]\}{\bigr \rangle }=\exp(-{\tfrac {1}{3}}{\sqrt {42}}\,\pi )}$ ${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[(2{\sqrt {7}}+3{\sqrt {3}})^{2}(2{\sqrt {2}}-{\sqrt {7}})^{2}]\}{\bigr \rangle }=\exp(-{\tfrac {1}{7}}{\sqrt {42}}\,\pi )}$ ${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[(2{\sqrt {7}}+3{\sqrt {3}})^{2}(2{\sqrt {2}}+{\sqrt {7}})^{2}]\}{\bigr \rangle }=\exp(-{\tfrac {1}{21}}{\sqrt {42}}\,\pi )}$

${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[({\sqrt {5}}-2)^{4}({\sqrt {2}}-1)^{6}]\}{\bigr \rangle }=\exp(-{\sqrt {70}}\,\pi )}$ ${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[({\sqrt {5}}-2)^{4}({\sqrt {2}}+1)^{6}]\}{\bigr \rangle }=\exp(-{\tfrac {1}{5}}{\sqrt {70}}\,\pi )}$ ${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[({\sqrt {5}}+2)^{4}({\sqrt {2}}-1)^{6}]\}{\bigr \rangle }=\exp(-{\tfrac {1}{7}}{\sqrt {70}}\,\pi )}$ ${\displaystyle q{\bigl \langle }\tan\{{\tfrac {1}{2}}\arctan[({\sqrt {5}}+2)^{4}({\sqrt {2}}+1)^{6}]\}{\bigr \rangle }=\exp(-{\tfrac {1}{35}}{\sqrt {70}}\,\pi )}$

The elliptic nome was explored by Richard Dedekind and this function is the fundament in the theory of eta functions and their related functions. The elliptic nome is the initial point of the construction of the Lambert series. In the theta function by Carl Gustav Jacobi the nome as an abscissa is assigned to algebraic combinations of the Arithmetic geometric mean and also the complete elliptic integral of the first kind. Many infinite series^[8] can be described easily in terms of the elliptic nome:

${\displaystyle \sum _{n=1}^{\infty }q(x)^{\Box (n)}={\tfrac {1}{2}}\vartheta _{00}[q(x)]-{\tfrac {1}{2}}={\tfrac {1}{2}}{\sqrt {2\pi ^{-1}K(x)}}-{\tfrac {1}{2}}={\tfrac {1}{2}}\operatorname {agm} (1-x;1+x)^{-1/2}-{\tfrac {1}{2}}}$

${\displaystyle \sum _{n=1}^{\infty }q(x)^{\Box (2n-1)}={\tfrac {1}{4}}\vartheta _{00}[q(x)]-{\tfrac {1}{4}}\vartheta _{01}[q(x)]={\tfrac {1}{4}}(1-{\sqrt[{4}]{1-x^{2}}}){\sqrt {2\pi ^{-1}K(x)}}}$

${\displaystyle \sum _{n=1}^{\infty }{\frac {2q(x)^{n}}{q(x)^{2n}+1}}={\tfrac {1}{2}}\vartheta _{00}[q(x)]^{2}-{\tfrac {1}{2}}=\pi ^{-1}K(x)-{\tfrac {1}{2}}}$

${\displaystyle \sum _{n=1}^{\infty }{\frac {2q(x)^{2n-1}}{q(x)^{4n-2}+1}}={\tfrac {1}{4}}\vartheta _{00}[q(x)]^{2}-{\tfrac {1}{4}}\vartheta _{01}[q(x)]^{2}={\tfrac {1}{2}}(1-{\sqrt {1-x^{2}}})\pi ^{-1}K(x)}$

${\displaystyle \sum _{n=1}^{\infty }\Box (n)q(x)^{\Box (n)}=2^{-1/2}\pi ^{-5/2}K(x)^{3/2}[E(x)-(1-x^{2})K(x)]}$

${\displaystyle \sum _{n=1}^{\infty }{\biggl [}{\frac {2q(x)^{n}}{1+q(x)^{2n}}}{\biggr ]}^{2}=2\pi ^{-2}E(x)K(x)-{\tfrac {1}{2}}}$

${\displaystyle \sum _{n=1}^{\infty }{\biggl [}{\frac {2q(x)^{n}}{1-q(x)^{2n}}}{\biggr ]}^{2}={\tfrac {2}{3}}\pi ^{-2}(2-x^{2})K(x)^{2}-2\pi ^{-2}K(x)E(x)+{\tfrac {1}{6}}}$