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Search: id:A052617
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| A052617 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 4, 18, 114, 936, 9480, 114480, 1607760, 25764480, 464123520, 9286099200, 204334099200, 4904497382400, 127523158963200, 3570735629260800, 107123376552192000, 3427968972460032000, 116551300751069184000
(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 562
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FORMULA
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E.g.f.: -(-x+x^2-1)/(-1+2*x)/(-1+x)
Recurrence: {a(0)=1, a(1)=4, (2*n^2+6*n+4)*a(n)+(-6-3*n)*a(n+1)+a(n+2), a(2)=18}
(-1+5*2^(n-1))*n!
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MAPLE
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spec := [S, {S=Prod(Union(Z, Sequence(Z)), Sequence(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: A113356 A062805 A053483 this_sequence A141714 A137567 A162224
Adjacent sequences: A052614 A052615 A052616 this_sequence A052618 A052619 A052620
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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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