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A052622
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E.g.f. (1-x^2)/(1-2x-x^2).
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0
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1, 2, 8, 60, 576, 6960, 100800, 1703520, 32901120, 714873600, 17258572800, 458324697600, 13277924352000, 416724685977600, 14084873439436800, 510058387238400000, 19702238017093632000, 808611973910028288000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 568
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FORMULA
| E.g.f.: (-1+x^2)/(-1+2*x+x^2)
Recurrence: {a(0)=1, a(1)=2, a(2)=8, (-2-n^2-3*n)*a(n) +(-4-2*n)*a(n+1) +a(n+2)=0}
Sum(-1/2*(-1+_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+_Z^2))*n!
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MAPLE
| spec := [S, {S=Sequence(Prod(Union(Z, Z), Sequence(Prod(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A027278 A001415 A053871 * A001188 A113145 A036794
Adjacent sequences: A052619 A052620 A052621 * A052623 A052624 A052625
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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