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Search: id:A052611
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| A052611 |
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A simple regular expression in a labeled universe. |
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+0
2
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| 1, 2, 12, 96, 1056, 14400, 236160, 4515840, 98703360, 2426941440, 66305433600, 1992646656000, 65328154214400, 2320237766246400, 88746105588940800, 3636883029491712000, 158978387626426368000, 7383729547341987840000
(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 556
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FORMULA
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E.g.f.: -1/(-1+2*x+2*x^2)
Recurrence: {a(0)=1, a(1)=2, (-2*n^2-6*n-4)*a(n)+(-4-2*n)*a(n+1)+a(n+2)}
Sum(1/6*(1+2*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+2*_Z^2))*n!
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MAPLE
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spec := [S, {S=Sequence(Union(Z, Z, Prod(Z, Union(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Equals 2^n * A080599(n).
Sequence in context: A052691 A014297 A052564 this_sequence A059864 A095338 A012548
Adjacent sequences: A052608 A052609 A052610 this_sequence A052612 A052613 A052614
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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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