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Search: id:A052634
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| A052634 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 1, 6, 18, 168, 840, 10800, 75600, 1249920, 11249280, 228614400, 2514758400, 60833203200, 790831641600, 22230464256000, 333456963840000, 10691545632768000, 181756275757056000, 6549628300959744000
(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 580
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FORMULA
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E.g.f.: 1/(-1+2*x^2)/(-1+x)
Recurrence: {a(1)=1, a(0)=1, a(2)=6, (12+2*n^3+12*n^2+22*n)*a(n)+(-2*n^2-10*n-12)*a(n+1)+(-n-3)*a(n+2)+a(n+3)}
(-1+Sum(1/2*(1+2*_alpha)*_alpha^(-1-n), _alpha =RootOf(-1+2*_Z^2)))*n!
n!*[2^floor(n/2+1)-1].
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MAPLE
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spec := [S, {S=Prod(Sequence(Prod(Z, Union(Z, Z))), Sequence(Z))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Adjacent sequences: A052631 A052632 A052633 this_sequence A052635 A052636 A052637
Sequence in context: A012774 A027744 A077531 this_sequence A059944 A052139 A052682
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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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