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Search: id:A052666
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| A052666 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 1, 8, 42, 456, 4800, 69840, 1093680, 20482560, 420577920, 9736070400, 245887488000, 6806133734400, 203555082931200, 6565920180019200, 226728504946944000, 8355118608764928000, 327047476385710080000
(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 613
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FORMULA
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E.g.f.: -1/(-1+x+3*x^2)
Recurrence: {a(1)=1, a(0)=1, (-3*n^2-9*n-6)*a(n)+(-2-n)*a(n+1)+a(n+2)}
Sum(1/13*(1+6*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+3*_Z^2))*n!
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MAPLE
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spec := [S, {S=Sequence(Union(Z, Prod(Z, Union(Z, Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Adjacent sequences: A052663 A052664 A052665 this_sequence A052667 A052668 A052669
Sequence in context: A047759 A047772 A020068 this_sequence A065789 A025064 A036424
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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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