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Search: id:A052606
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| A052606 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 2, 16, 180, 2688, 50160, 1123200, 29342880, 876072960, 29425939200, 1098191001600, 45083550758400, 2019049224192000, 97957525739673600, 5118154482618777600, 286518188551795200000, 17108806991486386176000
(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 551
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FORMULA
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E.g.f.: (-1+x)^2/(1-4*x+x^2)
Recurrence: {a(0)=1, a(1)=2, (n^2+3*n+2)*a(n)+(-4*n-8)*a(n+1)+a(n+2), a(2)=16}
Sum(-1/3*(-1+2*_alpha)*_alpha^(-1-n), _alpha=RootOf(1-4*_Z+_Z^2))*n!
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MAPLE
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spec := [S, {S=Sequence(Prod(Sequence(Z), Sequence(Z), Union(Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A155659 A108999 A138014 this_sequence A011553 A123898 A118644
Adjacent sequences: A052603 A052604 A052605 this_sequence A052607 A052608 A052609
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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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