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Search: id:A052988
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| A052988 |
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A simple regular expression. |
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+0
2
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| 1, 2, 5, 13, 33, 85, 218, 560, 1438, 3693, 9484, 24356, 62549, 160633, 412524, 1059409, 2720684, 6987029, 17943493, 46080951, 118341175, 303913730, 780485366, 2004376066, 5147467959, 13219288954, 33948652394, 87184038671
(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 1062
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FORMULA
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G.f.: -(-1+x^2)/(1-2*x-2*x^2+x^3+x^4)
Recurrence: {a(0)=1, a(1)=2, a(2)=5, a(3)=13, a(n)+a(n+1)-2*a(n+2)-2*a(n+3)+a(n+4)}
Sum(-1/331*(-49-147*_alpha+25*_alpha^2+76*_alpha^3)*_alpha^(-1-n), _alpha=RootOf(1-2*_Z-2*_Z^2+_Z^3+_Z^4))
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MAPLE
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spec := [S, {S=Sequence(Union(Prod(Union(Sequence(Prod(Z, Z)), 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: A077986 A007020 A080888 this_sequence A001429 A148288 A112841
Adjacent sequences: A052985 A052986 A052987 this_sequence A052989 A052990 A052991
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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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