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Search: id:A052687
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| A052687 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 2, 6, 18, 96, 480, 3600, 25200, 241920, 2177280, 25401600, 279417600, 3832012800, 49816166400, 784604620800, 11769069312000, 209227898880000, 3556874280960000, 70426110763008000, 1338096104497152000
(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 635
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FORMULA
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E.g.f.: -(-x+x^3-1)/(-1+x)/(-1+x^2)
Recurrence: {a(0)=1, a(1)=2, a(2)=6, (-n^3-8*n^2-17*n-10)*a(n)+(-2-n)*a(n+1)+(n+4)*a(n+2), a(3)=18}
(7/4+1/4*(-1)^(-n)+1/2*n)*n!
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MAPLE
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spec := [S, {S=Prod(Sequence(Z), Union(Z, Sequence(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: A053505 A000138 A028857 this_sequence A162059 A162060 A162061
Adjacent sequences: A052684 A052685 A052686 this_sequence A052688 A052689 A052690
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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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