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A052662
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E.g.f. (1-x^2)/(1-2x-x^2+x^3).
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0
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1, 2, 8, 54, 480, 5400, 72720, 1144080, 20563200, 415860480, 9344160000, 230958604800, 6227499801600, 181909958630400, 5722470212659200, 192874123233792000, 6934147333521408000, 264875092391669760000
(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 609
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FORMULA
| E.g.f.: -(-1+x^2)/(x^3-x^2-2*x+1)
Recurrence: {a(0)=1, a(1)=2, a(2)=8, (n^3+6*n^2+11*n+6)*a(n)+(-n^2-5*n-6)*a(n+1)+(-2*n-6)*a(n+2)+a(n+3)=0}
Sum(1/7*(2+_alpha)*_alpha^(-1-n), _alpha=RootOf(_Z^3-_Z^2-2*_Z+1))*n!
a(n) = n!*A052534(n). - R. J. Mathar, Nov 27 2011
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MAPLE
| spec := [S, {S=Sequence(Union(Z, Prod(Z, Sequence(Prod(Z, Z)))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A052694 A069729 A052599 * A073564 A199576 A005155
Adjacent sequences: A052659 A052660 A052661 * A052663 A052664 A052665
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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