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Search: id:A052925
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| A052925 |
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A simple regular expression. |
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+0
2
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| 2, 2, 4, 9, 22, 56, 145, 378, 988, 2585, 6766, 17712, 46369, 121394, 317812, 832041, 2178310, 5702888, 14930353, 39088170, 102334156, 267914297, 701408734, 1836311904, 4807526977, 12586269026, 32951280100, 86267571273
(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 910
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FORMULA
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G.f.: (-2+6*x-4*x^2+x^3)/(-1+x)/(1-3*x+x^2)
Recurrence: {a(2)=4, a(1)=2, a(0)=2, a(3)=9, -a(n)+3*a(n+1)-a(n+2)-1}
1+Sum(-1/5*(3*_alpha-2)*_alpha^(-1-n), _alpha=RootOf(_Z^2-3*_Z+1))
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MAPLE
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spec := [S, {S=Union(Sequence(Z), Sequence(Prod(Sequence(Z), Sequence(Z), Z)))}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Apart from first term, same as A055588.
Sequence in context: A100048 A052935 A166022 this_sequence A006182 A121623 A059473
Adjacent sequences: A052922 A052923 A052924 this_sequence A052926 A052927 A052928
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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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