OFFSET
1,1
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..2000
N. J. A. Sloane, Transforms
FORMULA
Product_{k>=1} (1+x^k)^a(k) = 1/(1-3x).
a(n) = 1/n*(3^n + Sum_{d<n and d|n} (-1)^(n/d)*d*a(d)).
EXAMPLE
(1+x)^3*(1+x^2)^6*(1+x^3)^8*(1+x^4)^24* ... = 1 + 3*x + 9*x^2 + 27*x^3 + 81*x^4 + ... .
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 23 2018
STATUS
approved