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Search: id:A052949
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| A052949 |
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A simple regular expression. |
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+0
2
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| 2, 2, 4, 7, 15, 32, 71, 158, 354, 794, 1783, 4005, 8998, 20217, 45426, 102070, 229348, 515339, 1157955, 2601900, 5846415, 13136774, 29518062, 66326482, 149034251, 334876921, 752461610, 1690765889, 3799116466, 8536537210, 19181424996
(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 1008
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FORMULA
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G.f.: -(2-4*x+x^3)/(x^3-x^2-2*x+1)/(-1+x)
Recurrence: {a(2)=4, a(1)=2, a(3)=7, a(0)=2, -a(n)+a(n+1)+2*a(n+2)-a(n+3)-1}
1+Sum(-1/7*(-2*_alpha+_alpha^2-1)*_alpha^(-1-n), _alpha=RootOf(_Z^3-_Z^2-2*_Z+1))
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MAPLE
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spec := [S, {S=Union(Sequence(Prod(Union(Sequence(Z), Z), Z)), Sequence(Z))}, unlabeled ]: seq(combstruct[count ](spec, size=n), n=0..20);
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CROSSREFS
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Equals A006356(n-1) + 1, n>0.
Sequence in context: A049904 A049906 A014265 this_sequence A014266 A032441 A065844
Adjacent sequences: A052946 A052947 A052948 this_sequence A052950 A052951 A052952
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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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