OFFSET
0,3
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 + 10*q^2 - 10*q^3 + 10*q^4 + 10*q^7 - 10*q^9 + 10*q^10 + 10*q^12 + ...
MATHEMATICA
a[ n_] := If[ n < 1, Boole[ n == 0], 10 Sum[ {0, 1, -1, 0, 0}[[ Mod[ d, 5, 1] ]] ], {d, Divisors @ n}]];
PROG
(PARI) {a(n) = if( n<1, n==0, 10 * sumdiv(n, d, (d%5==2) - (d%5==3)))};
(Sage) ModularForms( Gamma1(5), 1, prec=70).0;
(Magma) Basis( ModularForms( Gamma1(5), 1), 70) [1];
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Jun 13 2014
STATUS
approved