OFFSET
1,3
FORMULA
G.f.: Sum_{k>=1} k^(k-1)*x^k/(1 + x^k).
a(n) ~ n^(n-1). - Vaclav Kotesovec, Nov 09 2018
MATHEMATICA
Table[Sum[(-1)^(n/d + 1) d^(d - 1), {d, Divisors[n]}], {n, 21}]
nmax = 21; Rest[CoefficientList[Series[Sum[k^(k - 1) x^k/(1 + x^k), {k, 1, nmax}], {x, 0, nmax}], x]]
PROG
(PARI) a(n) = sumdiv(n, d, (-1)^(n/d+1)*d^(d-1)); \\ Michel Marcus, Nov 09 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Nov 08 2018
STATUS
approved