OFFSET
0,2
COMMENTS
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
FORMULA
Expansion of eta(q^2)^6 * eta(q^3)^5 / (eta(q)^3 * eta(q^6)^4) in powers of q.
Euler transform of period 6 sequence [ 3, -3, -2, -3, 3, -4, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (24 t)) = 27648^(1/2) (t/I)^2 g(t) where q = exp(2 Pi i t) and g() is the g.f. for A261445.
EXAMPLE
G.f. = 1 + 3*x + 3*x^2 - x^3 - 9*x^4 - 12*x^5 - 5*x^6 + 6*x^7 + 15*x^8 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ (1/2) x^(3/8) QPochhammer[ x^3]^3 EllipticTheta[ 2, 0, x^(1/2)]^3 / EllipticTheta[ 2, 0, x^(3/2)]^2, {x, 0, n}];
PROG
(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A)^6 * eta(x^3 + A)^5 / (eta(x + A)^3 * eta(x^6 + A)^4), n))};
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Nov 10 2015
STATUS
approved