A261444 Expansion of f(x^3)^2 * f(-x^6)^2 / f(-x^2) in powers of x where f() is a Ramanujan theta function.

1, 0, 1, 2, 2, 2, 0, 4, 2, 0, 1, 4, 4, 2, 2, 4, 5, 0, 2, 2, 6, 4, 2, 4, 6, 0, 0, 6, 4, 2, 4, 8, 7, 0, 2, 10, 4, 6, 0, 4, 6, 0, 1, 6, 8, 6, 4, 8, 4, 0, 4, 8, 10, 4, 2, 8, 8, 0, 2, 6, 12, 4, 4, 8, 8, 0, 5, 8, 6, 4, 0, 8, 14, 0, 2, 10, 8, 10, 2, 8, 11, 0, 6, 6, 6

Offset: 0

Author

Michael Somos, Aug 18 2015

Keywords

• nonn

Comments

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

Examples

			G.f. = 1 + x^2 + 2*x^3 + 2*x^4 + 2*x^5 + 4*x^7 + 2*x^8 + x^10 + ...
G.f. = q^2 + q^8 + 2*q^11 + 2*q^14 + 2*q^17 + 4*q^23 + 2*q^26 + ...
		

Links

• G. C. Greubel, Table of n, a(n) for n = 0..1000
• Michael Somos, Introduction to Ramanujan theta functions
• Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

Crossrefs

Cf. A261426.

Programs

Mathematica

a[ n_] := SeriesCoefficient[ QPochhammer[ -x^3]^2 QPochhammer[ x^6]^2 / QPochhammer[ x^2], {x, 0, n}];

PARI

{a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^6 + A)^8 / (eta(x^2 + A) * eta(x^3 + A)^2 * eta(x^12 + A)^2), n))};

Formula

Expansion of q^(-2/3) * eta(q^6)^8 / (eta(q^2) * eta(q^3)^2 * eta(q^12)^2) in powers of q.

Euler transform of period 12 sequence [ 0, 1, 2, 1, 0, -5, 0, 1, 2, 1, 0, -3, ...].

a(n) = A261426(2*n + 1).