A024420 a(n) = n! * Sum_{j=0..floor(n/2)} (-1)^j/binomial(n,j).

1, 1, 1, 4, 22, 108, 612, 4416, 36576, 331200, 3319200, 36806400, 445046400, 5813579520, 81716947200, 1230656716800, 19761225523200, 336973967769600, 6082189179494400, 115851849523200000, 2322322137354240000, 48869666136023040000

Offset: 0

Author

Clark Kimberling

Keywords

• nonn

Programs

Maple

a:= n-> n!*add((-1)^j/binomial(n, j), j=0..iquo(n, 2)):
seq(a(n), n=0..23);  # Alois P. Heinz, Jul 10 2019

Mathematica

Table[n!*Sum[(-1)^k/Binomial[n, k], {k, 0, Floor[n/2]}], {n, 0, 20}] (* Vaclav Kotesovec, Jul 10 2019 *)

Extensions

More terms from Sean A. Irvine, Jul 10 2019