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Search: id:A052667
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| A052667 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 2, 8, 48, 408, 4320, 54720, 806400, 13587840, 257644800, 5428684800, 125817753600, 3181049625600, 87128475033600, 2570016024576000, 81222270345216000, 2738060898693120000, 98070849049485312000
(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 615
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FORMULA
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E.g.f.: -1/(-1+2*x+x^4)
Recurrence: {a(0)=1, a(1)=2, a(2)=8, a(3)=48, (-n^4-35*n^2-50*n-24-10*n^3)*a(n)+(-2*n-8)*a(n+3)+a(n+4)}
Sum(1/86*(27+18*_alpha^3+12*_alpha^2+8*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+_Z^4))*n!
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MAPLE
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spec := [S, {S=Sequence(Union(Z, Z, Prod(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: A009812 A063075 A112541 this_sequence A006925 A005867 A079802
Adjacent sequences: A052664 A052665 A052666 this_sequence A052668 A052669 A052670
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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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