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A052670
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E.g.f. x^2/(1-4x).
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0
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0, 0, 2, 24, 384, 7680, 184320, 5160960, 165150720, 5945425920, 237817036800, 10463949619200, 502269581721600, 26118018249523200, 1462609021973299200, 87756541318397952000, 5616418644377468928000
(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 618
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FORMULA
| E.g.f.: -x^2/(-1+4*x)
Recurrence: {a(1)=0, a(0)=0, a(2)=2, (-4-4*n)*a(n)+a(n+1)=0}
4^(n-2)*n!, n>1.
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MAPLE
| spec := [S, {S=Prod(Z, Z, Sequence(Union(Z, Z, Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A090114 A188953 A081685 * A052736 A103904 A003102
Adjacent sequences: A052667 A052668 A052669 * A052671 A052672 A052673
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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