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Search: id:A052577
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| A052577 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 4, 26, 240, 2904, 43680, 786960, 16531200, 396789120, 10713669120, 321413702400, 10606692096000, 381841394457600, 14891820610867200, 625456552834713600, 28145546185236480000, 1350986237814140928000
(list; graph; listen)
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OFFSET
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0,2
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 520
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FORMULA
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E.g.f.: 1/(-1+x)/(-1+3*x)
Recurrence: {a(0)=1, a(1)=4, (3*n^2+9*n+6)*a(n)+(-4*n-8)*a(n+1)+a(n+2)}
(-1/2+1/2*3^(n+1))*n!
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MAPLE
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spec := [S, {S=Prod(Sequence(Z), Sequence(Union(Z, Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A000311 A001863 A115416 this_sequence A052880 A090357 A056786
Adjacent sequences: A052574 A052575 A052576 this_sequence A052578 A052579 A052580
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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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