A134340 Expansion of psi(x)^3 * f(-x^3)^3 / chi(-x)^2 in powers of x where psi(), chi(), f() are Ramanujan theta functions.

1, 5, 12, 22, 35, 50, 70, 92, 117, 145, 170, 210, 250, 287, 330, 362, 425, 477, 532, 600, 626, 715, 782, 850, 925, 962, 1100, 1162, 1247, 1335, 1370, 1520, 1617, 1750, 1810, 1850, 2040, 2147, 2262, 2380, 2451, 2625, 2752, 2882, 3015, 3005, 3290, 3500, 3577

Offset: 0

Author

Michael Somos, Oct 21 2007

Keywords

• nonn

Comments

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

Examples

			G.f. = 1 + 5*x + 12*x^2 + 22*x^3 + 35*x^4 + 50*x^5 + 70*x^6 + 92*x^7 + 117*x^8 + ...
G.f. = q^5 + 5*q^11 + 12*q^17 + 22*q^23 + 35*q^29 + 50*q^35 + 70*q^41 + 94*q^47 + ...
		

Links

• G. C. Greubel, Table of n, a(n) for n = 0..10000
• Michael Somos, Introduction to Ramanujan theta functions
• Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

Crossrefs

Cf. A103440, A109041.

Programs

Mathematica

a[ n_] := If[ n < 0, 0, (-1/24) DivisorSum[ 6 n + 5, #^2 KroneckerSymbol[ -3, #] &]]; (* Michael Somos, Oct 25 2015 *)
a[ n_] := SeriesCoefficient[ QPochhammer[ -x, x]^2 QPochhammer[ x^3]^3 EllipticTheta[ 2, 0, x^(1/2)]^3 / (8 x^(3/8)), {x, 0, n}]; (* Michael Somos, Oct 25 2015 *)

PARI

{a(n) = if( n<0, 0, n = 6*n + 5; sumdiv(n, d, d^2 * kronecker( -3, d)) / -24 )};

PARI

{a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A)^8 * eta(x^3 + A)^3 / eta(x + A)^5, n))};

Formula

Expansion of q^(-5/6) * eta(q^2)^8 * eta(q^3)^3 / eta(q)^5 in powers of q.

Euler transform of period 6 sequence [ 5, -3, 2, -3, 5, -6, ...].

-24 * a(n) = A103440(6*n + 5). 216 * a(n) = A109041(6*n + 5).