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Search: id:A052691
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| A052691 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 1, 2, 12, 96, 840, 8640, 105840, 1491840, 23587200, 413683200, 7983360000, 168129561600, 3835844812800, 94239732787200, 2480658276096000, 69651967537152000, 2077925954936832000, 65637135231123456000
(list; graph; listen)
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OFFSET
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0,3
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 639
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FORMULA
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E.g.f.: (-1+x)/(-1+2*x-x^2+x^3)
Recurrence: {a(1)=1, a(0)=1, a(2)=2, (-11*n-6-n^3-6*n^2)*a(n)+(n^2+5*n+6)*a(n+1)+(-2*n-6)*a(n+2)+a(n+3)}
Sum(1/23*(1+6*_alpha+3*_alpha^2)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z-_Z^2+_Z^3))*n!
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MAPLE
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spec := [S, {S=Sequence(Union(Z, Prod(Z, Z, Z, Sequence(Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Adjacent sequences: A052688 A052689 A052690 this_sequence A052692 A052693 A052694
Sequence in context: A074610 A103882 A003123 this_sequence A014297 A052564 A052611
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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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