OFFSET
1,2
FORMULA
a(n) = Sum_{k=1..n} Sum_{d|k} d^3 * tau(k/d).
G.f.: (1/(1-x)) * Sum_{k>=1} sigma_3(k) * x^k/(1 - x^k).
a(n) ~ Pi^8 * n^4 / 32400. - Vaclav Kotesovec, Aug 07 2022
MATHEMATICA
Table[Sum[DivisorSigma[3, k]*Floor[n/k], {k, 1, n}], {n, 1, 50}] (* Vaclav Kotesovec, Aug 07 2022 *)
PROG
(PARI) a(n) = sum(k=1, n, sigma(k, 3)*(n\k));
(PARI) a(n) = sum(k=1, n, sumdiv(k, d, d^3*numdiv(k/d)));
(PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=1, N, sigma(k, 3)*x^k/(1-x^k))/(1-x))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 24 2022
STATUS
approved