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A115977 Expansion of elliptic modular function lambda in powers of the nome q. 4
16, -128, 704, -3072, 11488, -38400, 117632, -335872, 904784, -2320128, 5702208, -13504512, 30952544, -68901888, 149403264, -316342272, 655445792, -1331327616, 2655115712, -5206288384, 10049485312, -19115905536, 35867019904, -66437873664 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700).

REFERENCES

M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math.Series 55, Tenth Printing, 1972, p. 591.

J. M. Borwein and P. B. Borwein, Pi and the AGM, Wiley, 1987, p. 121.

A. Erdelyi, Higher Transcendental Functions, McGraw-Hill, 1955, Vol. 3, p. 23, eq. (37).

LINKS

Table of n, a(n) for n=1..24.

M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].

M. Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

Eric Weisstein's World of Mathematics, Elliptic Lambda Function

FORMULA

Expansion of Jacobi elliptic m = k^2 = (theta_2(q) / theta_3(q))^4 in powers of the nome q.

Expansion of 16 * q * (psi(q^2) / phi(q))^4 = 16 * q * (psi(q^2) / psi(q))^8 = 16 * q * (psi(q) / phi(q))^8 = 16 * q * (psi(-q) / phi(-q^2))^8 = 16 * q / (chi(q) * chi(-q^2))^8 = 16 * q * (f(-q^4) / f(q))^8  in powers of q where phi(), psi(), chi(), f() are Ramanujan theta functions.

Expansion of 16 * (eta(q) * eta(q^4)^2 / eta(q^2)^3)^8 in powers of q.

G.f. A(x) satisfies 0 = f(A(x), A(x^2)) where f(u, v) = u^2 * (1 - v)^2 - 16 * v * (1 - u).

lambda( -1 / tau ) = 1 - lambda( tau ) (see A128692).

G.f. is a period 1 Fourier series which satisfies f(-1 / (4 t)) = g(t) where q = exp(2 pi i t) and g() is g.f. for A128692.

G.f.: 16 * q * (Product_{k>0} (1 + q^(2*k)) / (1 + q^(2*k - 1)))^8.

a(n) = 16 * A005798(n). a(n) = -(-1)^n * A014972(n) unless n=0.

Empirical : sum(exp(-2*Pi)^n*a(n),n=1..infinity) = 17-12*sqrt(2). Simon Plouffe, Feb. 20, 2011.

EXAMPLE

16*q - 128*q^2 + 704*q^3 - 3072*q^4 + 11488*q^5 - 38400*q^6 + 117632*q^7 - ...

MATHEMATICA

a[ n_] := If[ n < 0, 0, SeriesCoefficient[ InverseEllipticNomeQ @ x, {x, 0, n}]]

a[ n_] := If[ n < 0, 0, SeriesCoefficient[ ModularLambda[ Log[q] / (Pi I)], {q, 0, n}]]

a[ n_] := SeriesCoefficient[ (EllipticTheta[ 2, 0, q] / EllipticTheta[ 3, 0 , q])^4, {q, 0, n}]

PROG

(PARI) {a(n) = local(A); if( n<1, 0, n--; A = x * O(x^n); 16 * polcoeff( (eta(x + A) * eta(x^4 + A)^2 / eta(x^2 + A)^3)^8, n))}

CROSSREFS

Cf. A005798, A014972, A128692.

Sequence in context: A014972 * A128692 A132136 A163399 A067488 A120785

Adjacent sequences:  A115974 A115975 A115976 * A115978 A115979 A115980

KEYWORD

sign

AUTHOR

Michael Somos, Feb 09 2006

STATUS

approved

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Last modified September 19 03:51 EDT 2014. Contains 246967 sequences.