OFFSET
0,3
FORMULA
a(n) = n! * [x^n] exp( x * (1 - exp(n * x)) ).
a(n) = [x^n] Sum_{k>=0} (-x)^k / (1 - (n*k+1)*x)^(k+1).
a(n) = n! * Sum_{k=0..floor(n/2)} (-1)^k * n^(n-k) * Stirling2(n-k,k)/(n-k)!.
PROG
(PARI) a(n) = sum(k=0, n, (-1)^k*(k*n+1)^(n-k)*binomial(n, k));
(PARI) a(n) = n!*sum(k=0, n\2, (-1)^k*n^(n-k)*stirling(n-k, k, 2)/(n-k)!);
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Aug 29 2022
STATUS
approved