OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..1000
N. J. A. Sloane, Transforms
FORMULA
Product_{k>=1} (1-x^k)^(-a(k)) = 1 + Sum_{k>=1} A000290(k)*x^k.
G.f.: Sum_{k>=1} mu(k)*log(1 + x^k*(1 + x^k)/(1 - x^k)^3)/k. - Ilya Gutkovskiy, May 18 2019
EXAMPLE
(1-x)^(-1)*(1-x^2)^(-3)*(1-x^3)^(-5)*(1-x^4)^(-1)*(1-x^5)^6* ... = 1 + x + 4*x^2 + 9*x^3 + 16*x^4 + 25*x^5 + ... .
MAPLE
b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0,
add(binomial(a(i)+j-1, j)*b(n-i*j, i-1), j=0..n/i)))
end:
a:= proc(n) option remember; n^2-b(n, n-1) end:
seq(a(n), n=1..40); # Alois P. Heinz, Jun 29 2018
MATHEMATICA
b[n_, i_] := b[n, i] = If[n == 0, 1, If[i < 1, 0, Sum[Binomial[a[i] + j - 1, j]*b[n - i*j, i - 1], {j, 0, n/i}]]];
a[n_] := n^2 - b[n, n - 1];
a /@ Range[40] (* Jean-François Alcover, Jan 06 2020, after Alois P. Heinz *)
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Jun 25 2018
STATUS
approved