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Search: id:A052638
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| A052638 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 0, 0, 2, 18, 96, 960, 11520, 161280, 2580480, 46448640, 928972800, 20437401600, 490497638400, 12752938598400, 357082280755200, 10712468422656000, 342798989524992000, 11655165643849728000, 419585963178590208000
(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 584
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FORMULA
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E.g.f.: x^2*(-x+2*x^2-1)/(-1+2*x)
Recurrence: {a(1)=0, a(0)=0, a(2)=2, (-2*n-2)*a(n)+a(n+1), a(3)=18, a(4)=96}
1/4*2^n*n!
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MAPLE
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spec := [S, {S=Prod(Z, Z, Union(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: A070171 A036800 A052633 this_sequence A127553 A055357 A087291
Adjacent sequences: A052635 A052636 A052637 this_sequence A052639 A052640 A052641
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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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