OFFSET
0,3
FORMULA
a(n) = n! * Sum_{k=0..n} (3*(n-k)-1)^k / k!.
PROG
(PARI) a(n) = n!*sum(k=0, n, (3*(n-k)-1)^k/k!);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Dec 20 2023
STATUS
approved