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Search: id:A052670
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| A052670 |
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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, 24, 384, 7680, 184320, 5160960, 165150720, 5945425920, 237817036800, 10463949619200, 502269581721600, 26118018249523200, 1462609021973299200, 87756541318397952000, 5616418644377468928000
(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 618
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FORMULA
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E.g.f.: -x^2/(-1+4*x)
Recurrence: {a(1)=0, a(0)=0, a(2)=2, (-4-4*n)*a(n)+a(n+1)}
1/16*4^n*n!
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MAPLE
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spec := [S, {S=Prod(Z, Z, Sequence(Union(Z, Z, Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A126804 A090114 A081685 this_sequence A052736 A103904 A003102
Adjacent sequences: A052667 A052668 A052669 this_sequence A052671 A052672 A052673
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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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