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A052696 E.g.f. (1-x)^2/(1-4x+3x^2-x^3). 0
1, 2, 12, 114, 1440, 22680, 428400, 9439920, 237726720, 6735052800, 212012640000, 7341338188800, 277317497318400, 11348577278438400, 500138456661043200, 23615780481925632000, 1189441481702842368000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..16.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 645

FORMULA

E.g.f.: -(-1+x)^2/(-1+4*x-3*x^2+x^3)

Recurrence: {a(0)=1, a(1)=2, (-11*n-6-n^3-6*n^2)*a(n)+(18+3*n^2+15*n)*a(n+1) +(-4*n-12)*a(n+2) +a(n+3)=0, a(2)=12}

Sum(-1/31*(-4-7*_alpha+2*_alpha^2)*_alpha^(-1-n), _alpha=RootOf(-1+4*_Z-3*_Z^2+_Z^3))*n!

MAPLE

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

MATHEMATICA

With[{nn=20}, CoefficientList[Series[(1-x)^2/(1-4x+3x^2-x^3), {x, 0, nn}], x]Range[0, nn]!] (* Harvey P. Dale, Aug 28 2012 *)

CROSSREFS

Sequence in context: A091854 A141141 A128571 * A107723 A258175 A225797

Adjacent sequences:  A052693 A052694 A052695 * A052697 A052698 A052699

KEYWORD

easy,nonn

AUTHOR

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

STATUS

approved

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Last modified February 25 19:39 EST 2021. Contains 341618 sequences. (Running on oeis4.)