OFFSET
0,2
FORMULA
a(n) ~ 2 * n^(n-1). - Vaclav Kotesovec, Apr 22 2018
G.f.: exp(Sum_{k>=1} (sigma_k(2*k) - sigma_k(k))*x^k/(2^(k-1)*k)). - Ilya Gutkovskiy, Apr 14 2019
MATHEMATICA
nmax = 20; CoefficientList[Series[Product[((1 + (k*x)^k)/(1 - (k*x)^k))^(1/k), {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Apr 22 2018 *)
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
nonn
AUTHOR
Seiichi Manyama, Apr 22 2018
STATUS
approved