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A052653
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E.g.f. (1-2x^2)/(1-x-2x^2).
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0
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1, 1, 2, 18, 120, 1320, 15120, 216720, 3427200, 62052480, 1237420800, 27263174400, 653837184000, 17005993804800, 476080648243200, 14283727121664000, 457058345103360000, 15540339420942336000
(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 600
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FORMULA
| E.g.f.: (-1+2*x^2)/(-1+x+2*x^2)
Recurrence: {a(1)=1, a(0)=1, a(2)=2, (-2*n^2-6*n-4)*a(n)+(-2-n)*a(n+1)+a(n+2)=0}
Sum(-1/9*(-2+_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+2*_Z^2))*n!
a(n) = n!*A001045(n), n>0. - R. J. Mathar, Nov 27 2011
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MAPLE
| spec := [S, {S=Sequence(Prod(Z, Sequence(Prod(Z, Union(Z, Z)))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A058052 A119578 A052610 * A060589 A064447 A043022
Adjacent sequences: A052650 A052651 A052652 * A052654 A052655 A052656
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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