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Search: id:A052956
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| 2, 3, 6, 11, 21, 40, 77, 149, 290, 567, 1113, 2192, 4329, 8569, 16994, 33755, 67133, 133656, 266325, 531053, 1059522, 2114863, 4222961, 8434976, 16852241, 33675825, 67305282, 134535539, 268949685, 537702952, 1075088093, 2149661957
(list; graph; listen)
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OFFSET
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0,1
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 1027
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FORMULA
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G.f.: -(-2+3*x+x^2)/(-1+x+x^2)/(-1+2*x)
Recurrence: {a(2)=6, a(1)=3, a(0)=2, 2*a(n)+a(n+1)-3*a(n+2)+a(n+3)}
2^n+Sum(1/5*(1+2*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+_Z^2))
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MAPLE
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spec := [S, {S=Union(Sequence(Union(Prod(Z, Z), Z)), Sequence(Union(Z, Z)))}, unlabeled ]: seq(combstruct[count ](spec, size=n), n=0..20);
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CROSSREFS
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Cf. A000045, A000079.
Sequence in context: A079116 A109222 A006861 this_sequence A008930 A164362 A026742
Adjacent sequences: A052953 A052954 A052955 this_sequence A052957 A052958 A052959
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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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EXTENSIONS
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More terms from James A. Sellers (sellersj(AT)math.psu.edu), Jun 05 2000
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