OFFSET
0,2
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*x + x^2 - 2*x^7 + 2*x^8 + 2*x^10 - 2*x^11 + x^14 - 2*x^17 + ...
G.f. = q^9 - 2*q^17 + q^25 - 2*q^65 + 2*q^73 + 2*q^89 - 2*q^97 + q^121 + ...
MATHEMATICA
A244560[n_] := SeriesCoefficient[(QPochhammer[q^1, q^8]* QPochhammer[q^7, q^8]*QPochhammer[q^8, q^8])^2, {q, 0, n}]; Table[A244560[n], {n, 0, 50}] (* G. C. Greubel, Jun 17 2017 *)
PROG
(PARI) {a(n) = (-1)^n * sum(k=0, n, issquare(16*k + 9) * issquare(16*(n-k) + 9))};
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Jun 30 2014
STATUS
approved