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A305152
Expansion of Sum_{k>0} x^(k^2) / (1 + x^k).
4
1, -1, 1, 0, 1, -2, 1, 0, 2, -2, 1, -1, 1, -2, 2, 1, 1, -3, 1, -1, 2, -2, 1, 0, 2, -2, 2, -1, 1, -4, 1, 1, 2, -2, 2, -1, 1, -2, 2, 0, 1, -4, 1, -1, 3, -2, 1, 1, 2, -3, 2, -1, 1, -4, 2, 0, 2, -2, 1, -2, 1, -2, 3, 2, 2, -4, 1, -1, 2, -4, 1, 0, 1, -2, 3, -1, 2, -4, 1
OFFSET
1,6
LINKS
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
Cf. A038548, A048272, A193773 (odd bisection), A348608.
Sequence in context: A068913 A128306 A372626 * A170983 A113423 A131258
KEYWORD
sign
AUTHOR
Seiichi Manyama, May 26 2018
STATUS
approved