OFFSET
0,4
FORMULA
a(n) = n! * Sum_{k=1..floor(n/3)} (k-1)! * Stirling2(n-2*k,k)/(2^k * (n-2*k)!).
PROG
(PARI) a(n) = n!*sum(k=1, n\3, (k-1)!*stirling(n-2*k, k, 2)/(2^k*(n-2*k)!));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 14 2023
STATUS
approved