OFFSET
0,2
FORMULA
a(n) = n! * Sum_{k=0..n} (k+1)^(n-k) * binomial(k+3,3)/(n-k)!.
a(n) == 1 (mod 4).
PROG
(PARI) a(n) = n!*sum(k=0, n, (k+1)^(n-k)*binomial(k+3, 3)/(n-k)!);
CROSSREFS
KEYWORD
nonn,easy,new
AUTHOR
Seiichi Manyama, Jan 07 2025
STATUS
approved