OFFSET
0,3
COMMENTS
Exponential transform of A001157.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..505
FORMULA
a(0) = 1; a(n) = Sum_{k=1..n} sigma_2(k) * binomial(n-1,k-1) * a(n-k).
PROG
(PARI) my(N=40, x='x+O('x^N)); Vec(serlaplace(exp(sum(k=1, N, sigma(k, 2)*x^k/k!))))
(PARI) a(n) = if(n==0, 1, sum(k=1, n, sigma(k, 2)*binomial(n-1, k-1)*a(n-k)));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 29 2022
STATUS
approved