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Search: id:A052684
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| A052684 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 0, 4, 6, 96, 480, 6480, 60480, 887040, 11975040, 203212800, 3512678400, 69455232000, 1444668825600, 32953394073600, 796373690112000, 20671716409344000, 567677135241216000, 16550136029306880000
(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 632
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FORMULA
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E.g.f.: -1/(-1+2*x^2+x^3)
Recurrence: {a(1)=0, a(0)=1, a(2)=4, (-11*n-6-n^3-6*n^2)*a(n)+(-2*n^2-10*n-12)*a(n+1)+a(n+3)}
Sum(1/5*(-6+7*_alpha+8*_alpha^2)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z^2+_Z^3))*n!
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MAPLE
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spec := [S, {S=Sequence(Prod(Z, Union(Z, Z, 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: A012897 A013079 A087934 this_sequence A105037 A139730 A013023
Adjacent sequences: A052681 A052682 A052683 this_sequence A052685 A052686 A052687
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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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