OFFSET
0,4
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..2500
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of q^(-1/6) * eta(q^4) * eta(q^6)^5 / (eta(q^3) * eta(q^12))^2 in powers of q.
G.f. is a period 1 Fourier series which satisfies f(-1 / (576 t)) = 384^(1/2) (t/i) g(t) where q = exp(2 Pi i t) and g() is the g.f. for A226861.
G.f.: (Sum_{k in Z} x^(3*k^2)) * Product_{k>0} (1 - x^(4*k)).
a(4*n + 1) = a(4*n + 2) = 0. a(4*n) = A226289(n).
EXAMPLE
G.f. = 1 + 2*x^3 - x^4 - 2*x^7 - x^8 - 2*x^11 + 2*x^12 - 2*x^16 - x^20 + 2*x^23 + ...
G.f. = q + 2*q^19 - q^25 - 2*q^43 - q^49 - 2*q^67 + 2*q^73 - 2*q^97 - q^121 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ EllipticTheta[ 3, 0, q^3] QPochhammer[ q^4], {q, 0, n}];
PROG
(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^4 + A) * eta(x^6 + A)^5 / (eta(x^3 + A) * eta(x^12 + A))^2, n))};
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Jun 20 2013
STATUS
approved