OFFSET
1,2
FORMULA
a(n) = [x^n] Sum_{k>=1} (k * x)^k/(1 - x^k)^n.
MATHEMATICA
a[n_] := DivisorSum[n, (n/#)^(n/#) * Binomial[# + n - 2, n - 1] &]; Array[a, 20] (* Amiram Eldar, Apr 25 2021 *)
PROG
(PARI) a(n) = sumdiv(n, d, (n/d)^(n/d)*binomial(d+n-2, n-1));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 20 2021
STATUS
approved