OFFSET
1,6
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..5000
FORMULA
a(n) = Sum_{d|n, d <= sqrt(n)} (-1)^(d + n/d). - Ilya Gutkovskiy, Nov 02 2021
PROG
(PARI) {a(n) = polcoeff(sum(k=1, sqrtint(n), x^(k^2)/(1+x^k))+x*O(x^n), n)}
(PARI) a(n) = sumdiv(n, d, if (d <= sqrtint(n), (-1)^(d + n/d))); \\ Michel Marcus, Nov 03 2021
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, May 26 2018
STATUS
approved