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Search: id:A052649
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| A052649 |
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A simple regular expression in a labeled universe. |
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+0
3
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| 2, 5, 14, 54, 264, 1560, 10800, 85680, 766080, 7620480, 83462400, 997920000, 12933043200, 180583603200, 2702527027200, 43153254144000, 732297646080000, 13160434839552000, 249692574523392000
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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a(1) is 5, and gives the row number in the table of 0-origin permutations of order 3 in which the first 3 items are reversed. Row 5 of this table is 2 1 0. a(2) is 14, and gives the row number in the table of 0-origin permutations of order 4 in which the first three items are reversed. Row 14 of this table is 2 1 0 3.... a(6) is 10800, and gives the row number in the table of 0-origin permutations of order 8 in which the first 3 items are reversed. Row 10800 of this table is 2 1 0 3 4 5 6 7. Et cetera. - Eugene McDonnell (eemcd(AT)mac.com), Dec 03 2004
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 596
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FORMULA
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E.g.f.: -(-x+x^2-2)/(-1+x)^2
Recurrence: {a(1)=5, a(2)=14, a(0)=2, (-7*n-5-2*n^2)*a(n)+(3+2*n)*a(n+1)}
(3+2*n)*n!
a(n)=A129326(n), n>1. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 14 2008
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MAPLE
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spec := [S, {S=Prod(Sequence(Z), Union(Z, Sequence(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: A115275 A000679 A081439 this_sequence A122594 A047136 A047042
Adjacent sequences: A052646 A052647 A052648 this_sequence A052650 A052651 A052652
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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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