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A052696
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E.g.f. (1-x)^2/(1-4x+3x^2-x^3).
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0
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1, 2, 12, 114, 1440, 22680, 428400, 9439920, 237726720, 6735052800, 212012640000, 7341338188800, 277317497318400, 11348577278438400, 500138456661043200, 23615780481925632000, 1189441481702842368000
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OFFSET
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0,2
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LINKS
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Table of n, a(n) for n=0..16.
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 645
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FORMULA
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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!
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MAPLE
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spec := [S, {S=Sequence(Union(Z, Prod(Z, Sequence(Z), Sequence(Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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MATHEMATICA
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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 *)
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CROSSREFS
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Sequence in context: A091854 A141141 A128571 * A107723 A258175 A225797
Adjacent sequences: A052693 A052694 A052695 * A052697 A052698 A052699
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KEYWORD
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easy,nonn
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AUTHOR
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encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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STATUS
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approved
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