OFFSET
1,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..5000
EXAMPLE
G.f. = x - x^2 + 2*x^3 - x^4 + 2*x^7 - x^8 - x^9 + 2*x^11 - 2*x^14 + 2*x^15 + ...
MATHEMATICA
a[ n_] := If[ n < 0, 0, SeriesCoefficient[ Sum[ x^((k^2 + k)/2) / (1 + x^k), {k, Sqrt[8 n + 1]}], {x, 0, n}]];
PROG
(PARI) {a(n) = if( n<0, 0, polcoeff( sum(k=1, sqrtint(8*n + 1), x^((k^2 + k)/2) / (1 + x^k), x * O(x^n)), n))};
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Nov 05 2015
STATUS
approved