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Search: id:A052661
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| A052661 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 2, 1, 4, 12, 72, 480, 4320, 45360, 564480, 7983360, 127008000, 2235340800, 43110144000, 902918016000, 20399720140800, 494300911104000, 12783824621568000, 351419178958848000, 10230993181753344000
(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 608
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FORMULA
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E.g.f.: -(-2+3*x)/(-1+x+x^2)/(-1+x)
Recurrence: {a(1)=1, a(2)=4, a(0)=2, (n^3+6*n^2+11*n+6)*a(n)+(-2*n-6)*a(n+2)+a(n+3)}
(1+Sum(1/5*(-1+3*_alpha)*_alpha^(-1-n), _alpha =RootOf(-1+_Z+_Z^2)))*n!
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MAPLE
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spec := [S, {S=Union(Sequence(Z), Sequence(Prod(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: A111479 A088137 A064297 this_sequence A088624 A066409 A006173
Adjacent sequences: A052658 A052659 A052660 this_sequence A052662 A052663 A052664
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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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