OFFSET
0,4
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..2500
Amanda Clemm, Modular Forms and Weierstrass Mock Modular Forms, Mathematics, volume 4, issue 1, (2016)
FORMULA
EXAMPLE
G.f. = 1 - x - x^2 - 6*x^3 + 6*x^4 + 7*x^5 + 9*x^6 - 8*x^7 - 15*x^8 + ...
G.f. = q^-1 - q^2 - q^5 - 6*q^8 + 6*q^11 + 7*q^14 + 9*q^17 - 8*q^20 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ QPochhammer[ x] QPochhammer[ x^3]^6 / QPochhammer[ x^9]^3, {x, 0, n}];
PROG
(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x + A) * eta(x^3 + A)^6 / eta(x^9 + A)^3, n))};
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Dec 10 2016
STATUS
approved