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Search: id:A052693
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| A052693 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 2, 12, 102, 1176, 16920, 292320, 5891760, 135717120, 3517032960, 101268921600, 3207514464000, 110828037196800, 4148515981209600, 167232459621427200, 7222900141416960000, 332760193091149824000
(list; graph; listen)
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OFFSET
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0,2
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 642
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FORMULA
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E.g.f.: -(-1+x)/(1-3*x+x^3)
Recurrence: {a(0)=1, a(1)=2, (n^3+6*n^2+11*n+6)*a(n)+(-3*n-9)*a(n+2)+a(n+3), a(2)=12}
Sum(-1/9*(-2+_alpha^2-_alpha)*_alpha^(-1-n), _alpha=RootOf(1-3*_Z+_Z^3))*n!
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MAPLE
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spec := [S, {S=Sequence(Union(Z, Prod(Z, Union(Z, Sequence(Z)))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A137483 A113557 A123897 this_sequence A050621 A152254 A157328
Adjacent sequences: A052690 A052691 A052692 this_sequence A052694 A052695 A052696
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KEYWORD
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easy,nonn
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AUTHOR
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encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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