OFFSET
1,2
FORMULA
a(n) = Sum_{d|n} (n/d)^(d-1) * binomial(d+1,2).
MATHEMATICA
a[n_] := DivisorSum[n, (n/#)^(#-1) * Binomial[# + 1, 2] &]; Array[a, 50] (* Amiram Eldar, Jul 18 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, (n/d)^(d-1)*binomial(d+1, 2));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 13 2023
STATUS
approved