A052638 E.g.f. x^2*(1+x-2x^2)/(1-2x).

0, 0, 2, 18, 96, 960, 11520, 161280, 2580480, 46448640, 928972800, 20437401600, 490497638400, 12752938598400, 357082280755200, 10712468422656000, 342798989524992000, 11655165643849728000, 419585963178590208000

Offset

0,3

Links

Table of n, a(n) for n=0..18.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 584

Formula

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

Recurrence: {a(1)=0, a(0)=0, a(2)=2, (-2*n-2)*a(n)+a(n+1)=0, a(3)=18, a(4)=96}

1/4*2^n*n!

Maple

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

Mathematica

With[{nn=20}, CoefficientList[Series[x^2 (1+x-2x^2)/(1-2x), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Feb 29 2012 *)

Crossrefs

Sequence in context: A280157 A224616 A052633 * A127553 A055357 A087291

Adjacent sequences: A052635 A052636 A052637 * A052639 A052640 A052641

Keyword

easy,nonn

Author

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

Status

approved