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A052556
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E.g.f. 1/(1-x-x^3).
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0
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1, 1, 2, 12, 72, 480, 4320, 45360, 524160, 6894720, 101606400, 1636588800, 28740096000, 547977830400, 11245999564800, 247150455552000, 5795612798976000, 144409095806976000, 3809412354908160000
(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 497
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FORMULA
| E.g.f.: -1/(-1+x+x^3)
Recurrence: {a(1)=1, a(0)=1, a(2)=2, (-11*n-6-n^3-6*n^2)*a(n)+(-n-3)*a(n+2)+a(n+3)=0}
Sum(1/31*(4+6*_alpha^2+9*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+_Z^3))*n!
a(n) = n!*A000930(n). - R. J. Mathar, Nov 27 2011
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MAPLE
| spec := [S, {S=Sequence(Union(Z, Prod(Z, Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A167747 A018931 A062119 * A052833 A144086 A005443
Adjacent sequences: A052553 A052554 A052555 * A052557 A052558 A052559
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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