OFFSET
0,3
FORMULA
a(n) = n! * Sum_{k=1..floor(n/2)} k^(n-2*k-1)/(n-2*k)!.
a(n) ~ (n-1)! / (2^n *LambertW(1/2)^n). - Vaclav Kotesovec, Dec 29 2023
PROG
(PARI) a(n) = n!*sum(k=1, n\2, k^(n-2*k-1)/(n-2*k)!);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 14 2023
STATUS
approved