OFFSET
1,3
FORMULA
MATHEMATICA
a[n_] := Sum[(k - 1)^n * Sum[j^2, {j, 1, Floor[n/k]}], {k, 1, n}]; Array[a, 19] (* Amiram Eldar, Jul 30 2022 *)
PROG
(PARI) a(n) = sum(k=1, n, (k-1)^n*sum(j=1, n\k, j^2));
(PARI) a(n) = sum(k=1, n, k^2*(sigma(k, n-2)-(n\k)^n));
(PARI) a(n) = sum(k=1, n, k^2*sumdiv(k, d, (d-1)^n/d^2));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 30 2022
STATUS
approved