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A052656
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E.g.f. x*(1+2x-4x^2)/(1-2x).
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0
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0, 1, 8, 24, 192, 1920, 23040, 322560, 5160960, 92897280, 1857945600, 40874803200, 980995276800, 25505877196800, 714164561510400, 21424936845312000, 685597979049984000, 23310331287699456000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 603
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FORMULA
| E.g.f.: x*(-2*x+4*x^2-1)/(-1+2*x)
Recurrence: {a(1)=1, a(0)=0, (-2*n-2)*a(n)+a(n+1)=0, a(2)=8, a(3)=24}
2^(n-1)*n!, n>2.
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MAPLE
| spec := [S, {S=Prod(Z, Union(Z, Z, Sequence(Union(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A098070 A100042 A061027 * A094061 A182589 A002268
Adjacent sequences: A052653 A052654 A052655 * A052657 A052658 A052659
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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