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Search: id:A052981
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| A052981 |
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A simple regular expression. |
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+0
1
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| 1, 3, 15, 66, 300, 1353, 6114, 27615, 124743, 563475, 2545284, 11497332, 51934755, 234595164, 1059692925, 4786752927, 21622304991, 97670399970, 441188256072, 1992897309225, 9002142805206
(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 1054
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FORMULA
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G.f.: -(-1+x)/(1-4*x-3*x^2+3*x^3)
Recurrence: {a(0)=1, a(1)=3, a(2)=15, 3*a(n)-3*a(n+1)-4*a(n+2)+a(n+3)}
Sum(-1/95*(-11-22*_alpha+15*_alpha^2)*_alpha^(-1-n), _alpha=RootOf(1-4*_Z-3*_Z^2+3*_Z^3))
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MAPLE
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spec := [S, {S=Sequence(Prod(Union(Z, Z, Z), Union(Sequence(Z), Z)))}, unlabeled ]: seq(combstruct[count ](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A144067 A001447 A106732 this_sequence A086200 A122558 A110211
Adjacent sequences: A052978 A052979 A052980 this_sequence A052982 A052983 A052984
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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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