OFFSET
0,4
MATHEMATICA
a[n_] := n!*(1 + Sum[(-k*(n - k))^k/k!, {k, 1, n}]); Array[a, 18, 0] (* Amiram Eldar, Feb 19 2022 *)
PROG
(PARI) a(n) = n!*sum(k=0, n, (-k*(n-k))^k/k!);
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Feb 19 2022
STATUS
approved