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Search: id:A052636
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| A052636 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 2, 1, 6, 6, 120, 120, 6480, 5040, 685440, 362880, 119750400, 39916800, 31135104000, 6227020800, 11245999564800, 1307674368000, 5377157001216000, 355687428096000, 3284417711038464000
(list; graph; listen)
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OFFSET
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0,1
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 582
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FORMULA
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E.g.f.: -(-2+x+2*x^2)/(-1+2*x^2)/(-1+x)
Recurrence: {a(1)=1, a(2)=6, a(0)=2, (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*_alpha^(-n), _alpha=RootOf(-1+2*_Z^2)))*n!
n!*[2^(n/2)+1] if n is even, n! otherwise.
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MAPLE
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spec := [S, {S=Union(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: A052633 A052634 A052635 this_sequence A052637 A052638 A052639
Sequence in context: A113979 A053442 A019082 this_sequence A084312 A066752 A059364
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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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