A024420 - OEIS

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

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OFFSET

0,4

LINKS

Table of n, a(n) for n=0..21.

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 *)

CROSSREFS

Sequence in context: A184701 A001436 A224243 * A220457 A108840 A007994

Adjacent sequences: A024417 A024418 A024419 * A024421 A024422 A024423

KEYWORD

nonn

AUTHOR

Clark Kimberling

EXTENSIONS

More terms from Sean A. Irvine, Jul 10 2019

STATUS

approved