OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..6290
FORMULA
G.f.: Sum_{k>0} x^k/(1-k*x^k).
From Seiichi Manyama, Jun 17 2019: (Start)
L.g.f.: -log(Product_{k>=1} (1 - k*x^k)^(1/k^2)) = Sum_{k>=1} a(k)*x^k/k.
a(p) = 2 for prime p. (End)
MATHEMATICA
a[n_]:= DivisorSum[n, (n/#)^(#-1) &]; Array[a, 30] (* G. C. Greubel, May 16 2018 *)
PROG
(PARI) a(n)=sumdiv(n, d, d^(n/d-1) ); /* Joerg Arndt, Oct 07 2012 */
(PARI) N=66; x='x+O('x^N); Vec(x*deriv(-log(prod(k=1, N, (1-k*x^k)^(1/k^2))))) \\ Seiichi Manyama, Jun 17 2019
CROSSREFS
KEYWORD
nonn,look
AUTHOR
Vladeta Jovovic, Oct 15 2003
STATUS
approved