OFFSET
0,2
FORMULA
E.g.f. A(x) satisfies A(x) = (1 + x*A(x))^3 * exp(x * A(x)).
a(n) = n! * Sum_{k=0..n} (n+1)^(k-1) * binomial(3*n+3,n-k)/k!.
PROG
(PARI) a(n) = n!*sum(k=0, n, (n+1)^(k-1)*binomial(3*n+3, n-k)/k!);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Nov 09 2024
STATUS
approved