OFFSET
0,5
FORMULA
a(n) = n! * Sum_{k=1..floor(n/4)} (k-1)! * |Stirling1(n-3*k,k)|/(n-3*k)!.
PROG
(PARI) a(n) = n!*sum(k=1, n\4, (k-1)!*abs(stirling(n-3*k, k, 1))/(n-3*k)!);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 15 2023
STATUS
approved