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Search: id:A052554
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| A052554 |
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E.g.f.: (1-x)/(1-x-x^2). |
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+0
1
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| 1, 0, 2, 6, 48, 360, 3600, 40320, 524160, 7620480, 123379200, 2195424000, 42631142400, 896690995200, 20312541849600, 492993236736000, 12762901831680000, 351063491530752000, 10224590808047616000
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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A simple regular expression in a labeled universe.
Number of ways to use the elements of {1,..,n} once each to form a sequence of lists, each having length at least 2. - Bob Proctor, Apr 19, 2005
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 493
Index entries for related partition-counting sequences
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FORMULA
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Recurrence: {a(1)=0, a(0)=1, (-2-n^2-3*n)*a(n)+(-2-n)*a(n+1)+a(n+2)}
Sum(1/5*(-1+3*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+_Z^2))*n!
a(n) = n!*Fibonacci(n-1) for n >= 1. - Bob Proctor, Apr 19, 2005
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MAPLE
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spec := [S, {S=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: A092143 A052593 A052586 this_sequence A052743 A052587 A052735
Adjacent sequences: A052551 A052552 A052553 this_sequence A052555 A052556 A052557
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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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