OFFSET
0,3
FORMULA
a(n) = Sum_{k=0..floor(n/4)} (-1)^k * (n-3*k)! * binomial(n-3*k,k).
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(sum(k=0, N, k!*(x*(1-x^3))^k))
(PARI) a(n) = sum(k=0, n\4, (-1)^k*(n-3*k)!*binomial(n-3*k, k));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Feb 20 2024
STATUS
approved