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Search: id:A052686
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| A052686 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 0, 0, 2, 24, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600, 6227020800, 87178291200, 1307674368000, 20922789888000, 355687428096000, 6402373705728000, 121645100408832000, 2432902008176640000
(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 634
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FORMULA
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E.g.f.: x^2*(-3*x+3*x^2-1)/(-1+x)
Recurrence: {a(1)=0, a(0)=0, (-1-n)*a(n)+a(n+1), a(2)=2, a(4)=24, a(3)=24}
n!
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MAPLE
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spec := [S, {S=Prod(Z, Z, Union(Z, 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: A002743 A055535 A072217 this_sequence A064818 A022374 A139334
Adjacent sequences: A052683 A052684 A052685 this_sequence A052687 A052688 A052689
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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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