OFFSET
0,2
FORMULA
a(n) = Sum_{k=0..n} 3^(n-k) * (Product_{j=0..k-1} (3*j+2)) * Stirling1(n,k).
a(0) = 1; a(n) = Sum_{k=1..n} (-3)^k * (1/3 * k/n - 1) * (k-1)! * binomial(n,k) * a(n-k).
PROG
(PARI) a(n) = sum(k=0, n, 3^(n-k)*prod(j=0, k-1, 3*j+2)*stirling(n, k, 1));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Nov 18 2023
STATUS
approved