OFFSET
0,4
FORMULA
a(n) = -n! * Sum_{k=0..n} (-3*n+2*k-1)^(n-k-1) * binomial(3*n-k,k)/(n-k)!.
PROG
(PARI) a(n) = -n!*sum(k=0, n, (-3*n+2*k-1)^(n-k-1)*binomial(3*n-k, k)/(n-k)!);
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Jan 05 2025
STATUS
approved