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Search: id:A052545
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| A052545 |
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A simple regular expression. |
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+0
1
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| 1, 1, 4, 11, 32, 92, 265, 763, 2197, 6326, 18215, 52448, 151018, 434839, 1252069, 3605189, 10380728, 29890115, 86065156, 247814740, 713554105, 2054597159, 5915976737, 17034376106, 49048531159, 141229616740, 406654474114
(list; graph; listen)
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OFFSET
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0,3
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 481
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FORMULA
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G.f.: (-1+x)^2/(1-3*x+x^3)
Recurrence: {a(1)=1, a(0)=1, a(2)=4, a(n)-3*a(n+2)+a(n+3)}
Sum(-1/9*(-1+2*_alpha^2-2*_alpha)*_alpha^(-1-n), _alpha=RootOf(1-3*_Z+_Z^3))
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MAPLE
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spec := [S, {S=Sequence(Prod(Z, Union(Z, Sequence(Z)), Sequence(Z)))}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A027153 A034754 A038747 this_sequence A025268 A149232 A149233
Adjacent sequences: A052542 A052543 A052544 this_sequence A052546 A052547 A052548
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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 06 2000
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