OFFSET
0,4
FORMULA
a(n) = n! * Sum_{k=0..floor(n/2)} (-1)^k * binomial(n-k-1,k)/(n-2*k)!.
a(n) == 1 mod 6.
PROG
(PARI) a(n) = n!*sum(k=0, n\2, (-1)^k*binomial(n-k-1, k)/(n-2*k)!);
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Jun 09 2024
STATUS
approved