OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1930
FORMULA
a(n) = Sum_{k=0..n} A257673(n,k).
a(n) ~ c * d^n, where d = 3.2975132503126723336836261261699651439543806296893328114462016186843..., c = 0.3713883419445088444000361183895708557141471246022776707501762842135... . - Vaclav Kotesovec, May 19 2015
G.f.: 1/(2 - Product_{k>=1} 1/(1 - x^k)^k). - Ilya Gutkovskiy, Oct 18 2018
MAPLE
g:= proc(n) option remember; `if`(n=0, 1, add(
g(n-j)*numtheory[sigma][2](j), j=1..n)/n)
end:
a:= proc(n) option remember; `if`(n=0, 1,
add(a(n-i)*g(i), i=1..n))
end:
seq(a(n), n=0..36);
MATHEMATICA
g[n_] := g[n] = If[n==0, 1, Sum[g[n-j] DivisorSigma[2, j], {j, 1, n}]/n];
a[n_] := a[n] = If[n==0, 1, Sum[a[n-i] g[i], {i, 1, n}]];
Table[a[n], {n, 0, 36}] (* Jean-François Alcover, Aug 22 2021, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, May 03 2015
STATUS
approved