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
EXAMPLE
G.f. = 1 - 2*q - 6*q^4 + 16*q^5 + 8*q^8 - 50*q^9 + 16*q^12 + 80*q^13 + ...
MATHEMATICA
a[n_]:= SeriesCoefficient[EllipticTheta[3, 0, -q]*EllipticTheta[3, 0, -q^4 ]^4, {q, 0, n}]; (* corrected by G. C. Greubel, Mar 15 2018 *)
PROG
(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x + A)^2 * eta(x^4 + A)^8 / (eta(x^2 + A) * eta(x^8 + A)^4), n))};
(Magma) A := Basis( ModularForms( Gamma0(8), 5/2), 68); A[1] - 2*A[2];
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Sep 01 2014
STATUS
approved