OFFSET
0,2
FORMULA
a(0) = 1; a(n) = 3*a(n-1) + n!.
a(n) = (n+3)*a(n-1) - 3*n*a(n-2).
a(n) ~ n!. - Vaclav Kotesovec, Jan 13 2024
PROG
(PARI) a(n) = sum(k=0, n, k!*3^(n-k));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Dec 29 2023
STATUS
approved