A052598 E.g.f. (1-x)/(1-x-2x^2).

1, 0, 4, 12, 144, 1200, 15840, 211680, 3467520, 61689600, 1241049600, 27223257600, 654316185600, 16999766784000, 476167826534400, 14282419447296000, 457079267893248000, 15539983733514240000

Offset

0,3

Links

Table of n, a(n) for n=0..17.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 543

Formula

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

Recurrence: {a(1)=0, a(0)=1, (-2*n^2-6*n-4)*a(n)+(-2-n)*a(n+1)+a(n+2)=0}

Sum(1/9*(-1+5*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+2*_Z^2))*n!

a(n) = n!*A078008(n). - R. J. Mathar, Nov 27 2011

Maple

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

Mathematica

With[{nn=20}, CoefficientList[Series[(1-x)/(1-x-2x^2), {x, 0, nn}], x] Range[ 0, nn]!] (* Harvey P. Dale, Sep 06 2020 *)

Crossrefs

Sequence in context: A204321 A152121 A077611 * A230691 A032071 A365310

Adjacent sequences: A052595 A052596 A052597 * A052599 A052600 A052601

Keyword

easy,nonn

Author

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

Status

approved