OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..5000
FORMULA
G.f.: (1/(1 - x)) * Sum_{k>=1} k*x^k * (1 - x^k)/(1 - k*x^k).
a(n) ~ 3^((n - mod(n,3))/3). - Vaclav Kotesovec, Jun 11 2021
MATHEMATICA
a[n_] := Sum[k^Floor[n/k], {k, 1, n}]; Array[a, 40] (* Amiram Eldar, Jun 08 2021 *)
PROG
(PARI) a(n) = sum(k=1, n, k^(n\k));
(PARI) my(N=66, x='x+O('x^N)); Vec(sum(k=1, N, k*x^k*(1-x^k)/(1-k*x^k))/(1-x))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 08 2021
STATUS
approved