OFFSET
0,2
FORMULA
a(n) ~ -2 * n^(n-1). - Vaclav Kotesovec, Apr 25 2018
G.f.: exp(Sum_{k>=1} (sigma_k(k) - sigma_k(2*k))*x^k/(2^(k-1)*k)). - Ilya Gutkovskiy, Apr 14 2019
PROG
(PARI) N=66; x='x+O('x^N); Vec(prod(k=1, N, ((1-(k*x)^k)/(1+(k*x)^k))^(1/k)))
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Apr 22 2018
STATUS
approved