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A052594
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E.g.f. x(1+x-2x^2)/(1-2x).
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0
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0, 1, 6, 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 539
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FORMULA
| E.g.f.: x*(-x+2*x^2-1)/(-1+2*x)
Recurrence: {a(1)=1, a(0)=0, (-2*n-2)*a(n)+a(n+1)=0, a(2)=6, a(3)=24}
2^(n-1)*n!, n>2.
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MAPLE
| spec := [S, {S=Prod(Z, Union(Z, Sequence(Union(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A038033 A064049 A018981 * A091097 A112675 A052583
Adjacent sequences: A052591 A052592 A052593 * A052595 A052596 A052597
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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