OFFSET
1,3
FORMULA
MATHEMATICA
a[n_] := Sum[(k - 1)^n * Binomial[Floor[n/k]+1, 2], {k, 1, n}]; Array[a, 18] (* Amiram Eldar, Jul 28 2022 *)
PROG
(PARI) a(n) = sum(k=1, n, (k-1)^n*binomial((n\k)+1, 2));
(PARI) a(n) = sum(k=1, n, k*(sigma(k, n-1)-(n\k)^n));
(PARI) a(n) = sum(k=1, n, k*sumdiv(k, d, (d-1)^n/d));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 27 2022
STATUS
approved