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Search: id:A052574
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| A052574 |
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A simple regular expression in a labeled universe. |
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+0
1
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| 1, 1, 4, 30, 312, 4080, 64080, 1174320, 24595200, 579519360, 15172012800, 436929292800, 13726748851200, 467182235520000, 17123385600921600, 672444082582272000, 28167703419727872000, 1253648083943743488000
(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 517
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FORMULA
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E.g.f.: -(-1+2*x)/(1-3*x+x^2)
Recurrence: {a(1)=1, a(0)=1, (n^2+3*n+2)*a(n)+(-6-3*n)*a(n+1)+a(n+2)}
Sum(1/5*(-1+4*_alpha)*_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(Prod(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: A052452 A088794 A145348 this_sequence A158834 A139086 A128329
Adjacent sequences: A052571 A052572 A052573 this_sequence A052575 A052576 A052577
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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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