OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = [x^n] Sum_{k>=1} k * x^k/(1 - x^k)^n.
a(n) = [x^n] Sum_{k>=1} binomial(k+n-2,n-1) * x^k/(1 - x^k)^2.
MATHEMATICA
a[n_] := n * DivisorSum[n, Binomial[# + n - 2, n-1]/# &]; Array[a, 30] (* Amiram Eldar, Apr 25 2021 *)
PROG
(PARI) a(n) = n*sumdiv(n, d, binomial(d+n-2, n-1)/d);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 19 2021
STATUS
approved