OFFSET
0,6
FORMULA
a(n) = n! * Sum_{k=0..floor(n/4)} binomial(3*n/4-2*k-1,k)/(n-4*k)!.
a(n) == 1 mod 90.
PROG
(PARI) a(n) = n!*sum(k=0, n\4, binomial(3*n/4-2*k-1, k)/(n-4*k)!);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 08 2024
STATUS
approved