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A052646
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E.g.f. 1/((1-x)(1-x-x^2)).
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0
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1, 2, 8, 42, 288, 2400, 23760, 272160, 3548160, 51891840, 841881600, 15008716800, 291711974400, 6139842508800, 139136552755200, 3377722892544000, 87457261731840000, 2405869763641344000
(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 592
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FORMULA
| E.g.f.: 1/(-1+x)/(-1+x+x^2)
Recurrence: {a(0)=1, a(1)=2, a(2)=8, (n^3+6*n^2+11*n+6)*a(n)+(-2*n-6)*a(n+2)+a(n+3)=0}
(-1+Sum(1/5*(4+3*_alpha)*_alpha^(-1-n), _alpha =RootOf(-1+_Z+_Z^2)))*n!
n!*Sum(k=0, n, A000045(n+1)).
a(n) = n!*A000071(n+3). - R. J. Mathar, Nov 27 2011
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MAPLE
| spec := [S, {S=Prod(Sequence(Z), Sequence(Union(Z, Prod(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A121635 A002874 A078592 * A002856 A093461 A191994
Adjacent sequences: A052643 A052644 A052645 * A052647 A052648 A052649
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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