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Search: id:A052990
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| A052990 |
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A simple regular expression. |
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+0
1
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| 1, 3, 13, 53, 219, 903, 3725, 15365, 63379, 261431, 1078373, 4448165, 18348171, 75684103, 312188253, 1287740773, 5311783139, 21910496823, 90378288885, 372800086085, 1537757639579
(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 1064
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FORMULA
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G.f.: -(-1+x)/(1-4*x-x^2+2*x^3)
Recurrence: {a(0)=1, a(1)=3, a(2)=13, 2*a(n)-a(n+1)-4*a(n+2)+a(n+3)}
Sum(-1/142*(-22+18*_alpha^2-21*_alpha)*_alpha^(-1-n), _alpha=RootOf(1-4*_Z-_Z^2+2*_Z^3))
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MAPLE
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spec := [S, {S=Sequence(Union(Prod(Union(Sequence(Z), Z), Union(Z, Z)), Z))}, unlabeled ]: seq(combstruct[count ](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A065059 A072197 A065838 this_sequence A151209 A151210 A151211
Adjacent sequences: A052987 A052988 A052989 this_sequence A052991 A052992 A052993
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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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