OFFSET
0,3
FORMULA
a(n) = (n-1) * a(n-1) + (n-2) * a(n-2) + (n-3) * a(n-3) + (n-4) * a(n-4) + (n-8) * a(n-5) - 4 * a(n-6) - 4 * a(n-7) - 4 * a(n-8) - 4 * a(n-9) + 5 for n > 8.
G.f.: Sum_{k>=0} k! * x^k/(1-x^5)^(k+1). - Seiichi Manyama, Feb 26 2024
PROG
(PARI) a(n) = sum(k=0, n\5, (n-4*k)!/k!);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Nov 19 2022
STATUS
approved