OFFSET
1,2
FORMULA
a(n) = [x^n] Sum_{k>0} (n * x)^k / (1 - (k * x)^k).
If p is prime, a(p) = p + p^p.
MATHEMATICA
a[n_] := DivisorSum[n, #^n * (n/#)^# &]; Array[a, 20] (* Amiram Eldar, Aug 09 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, d^n*(n/d)^d);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jan 16 2023
STATUS
approved