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Search: id:A052557
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| A052557 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 0, 0, 6, 24, 120, 1440, 15120, 161280, 2177280, 32659200, 518918400, 9101030400, 174356582400, 3574309939200, 78460462080000, 1841205510144000, 45883678224384000, 1210048630382592000
(list; graph; listen)
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OFFSET
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0,4
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 499
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FORMULA
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E.g.f.: (-1+x)/(-1+x+x^3)
Recurrence: {a(1)=0, a(0)=1, a(2)=0, (-11*n-6-n^3-6*n^2)*a(n)+(-n-3)*a(n+2)+a(n+3)}
Sum(-1/31*(2+3*_alpha^2-11*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+_Z^3))*n!
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MAPLE
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spec := [S, {S=Sequence(Prod(Z, Z, Z, Sequence(Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A050212 A047865 A060249 this_sequence A052170 A027224 A110707
Adjacent sequences: A052554 A052555 A052556 this_sequence A052558 A052559 A052560
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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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