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Search: id:A052668
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| A052668 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 3, 18, 168, 2088, 32400, 603360, 13109040, 325503360, 9092684160, 282219033600, 9635476435200, 358879494758400, 14480588157235200, 629228583138355200, 29295027261916416000, 1454816084780298240000
(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 616
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FORMULA
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E.g.f.: -1/(-1+3*x+x^3)
Recurrence: {a(0)=1, a(1)=3, a(2)=18, (-11*n-6-n^3-6*n^2)*a(n)+(-3*n-9)*a(n+2)+a(n+3)}
Sum(1/15*(4+_alpha+2*_alpha^2)*_alpha^(-1-n), _alpha=RootOf(-1+3*_Z+_Z^3))*n!
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MAPLE
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spec := [S, {S=Sequence(Union(Z, Z, Z, Prod(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: A107403 A053513 A138211 this_sequence A121423 A074932 A101483
Adjacent sequences: A052665 A052666 A052667 this_sequence A052669 A052670 A052671
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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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