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Search: id:A052608
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| A052608 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 1, 6, 42, 408, 4920, 71280, 1204560, 23264640, 505491840, 12203654400, 324084499200, 9388910361600, 294668851276800, 9959509521561600, 360665744414976000, 13931586106454016000, 571775010100310016000
(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 553
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FORMULA
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E.g.f.: (-1+x)/(-1+2*x+x^2)
Recurrence: {a(1)=1, a(0)=1, (-2-n^2-3*n)*a(n)+(-4-2*n)*a(n+1)+a(n+2)}
Sum(1/2*_alpha^(-n), _alpha=RootOf(-1+2*_Z+_Z^2))*n!
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MAPLE
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spec := [S, {S=Sequence(Prod(Sequence(Z), Union(Z, Prod(Z, Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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MATHEMATICA
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Table[LucasL[n, 2]*n!/2, {n, 0, 17}] [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jul 09 2009]
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CROSSREFS
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Sequence in context: A135887 A052589 A074107 this_sequence A098461 A034662 A074651
Adjacent sequences: A052605 A052606 A052607 this_sequence A052609 A052610 A052611
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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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