A052645 E.g.f. 2*x^2*(1+x-x^2)/(1-x).

0, 0, 4, 24, 48, 240, 1440, 10080, 80640, 725760, 7257600, 79833600, 958003200, 12454041600, 174356582400, 2615348736000, 41845579776000, 711374856192000, 12804747411456000, 243290200817664000

Offset

0,3

Links

Table of n, a(n) for n=0..19.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 591

Formula

E.g.f.: 2*x^2*(-x+x^2-1)/(-1+x)

Recurrence: {a(1)=0, a(0)=0, (-1-n)*a(n)+a(n+1)=0, a(2)=4, a(3)=24, a(4)=48}

2*n!, n>3.

Maple

spec := [S, {S=Prod(Z, Union(Z, Z), Union(Z, Sequence(Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);

Mathematica

With[{nn=20}, CoefficientList[Series[2x^2 (1+x-x^2)/(1-x), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, May 14 2017 *)

Crossrefs

Sequence in context: A039935 A090821 A226575 * A353250 A191778 A157625

Adjacent sequences: A052642 A052643 A052644 * A052646 A052647 A052648

Keyword

easy,nonn

Author

encyclopedia(AT)pommard.inria.fr, Jan 25 2000

Status

approved