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Search: id:A052567
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| A052567 |
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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, 48, 504, 6600, 103680, 1900080, 39795840, 937681920, 24548832000, 706966444800, 22210346188800, 755916735974400, 27706219904563200, 1088037381150720000, 45576301518139392000, 2028445209752113152000
(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 509
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FORMULA
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E.g.f.: (-1+x)^2/(1-3*x+x^2)
Recurrence: {a(1)=1, a(0)=1, a(2)=6, (n^2+3*n+2)*a(n)+(-6-3*n)*a(n+1)+a(n+2)}
Sum(-1/5*(3*_alpha-2)*_alpha^(-1-n), _alpha=RootOf(_Z^2-3*_Z+1))*n!
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MAPLE
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spec := [S, {S=Sequence(Prod(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: A052639 A053506 A055861 this_sequence A002170 A052731 A052711
Adjacent sequences: A052564 A052565 A052566 this_sequence A052568 A052569 A052570
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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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