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Search: id:A052595
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| A052595 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 3, 20, 198, 2616, 43200, 856080, 19792080, 522950400, 15544690560, 513406252800, 18652322304000, 739253228313600, 31740638183654400, 1467650891266560000, 72709824125562624000, 3842307771930980352000
(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 540
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FORMULA
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E.g.f.: -1/(-1+3*x+x^2)
Recurrence: {a(0)=1, a(1)=3, (-2-n^2-3*n)*a(n)+(-6-3*n)*a(n+1)+a(n+2)}
Sum(1/13*(2*_alpha+3)*_alpha^(-1-n), _alpha=RootOf(-1+3*_Z+_Z^2))*n!
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MAPLE
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spec := [S, {S=Sequence(Union(Z, Z, Z, Prod(Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A087152 A158833 A054361 this_sequence A052590 A081209 A014068
Adjacent sequences: A052592 A052593 A052594 this_sequence A052596 A052597 A052598
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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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