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Search: id:A052908
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| A052908 |
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A simple regular expression. |
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+0
1
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| 1, 1, 2, 4, 9, 19, 40, 85, 180, 381, 807, 1709, 3619, 7664, 16230, 34370, 72785, 154136, 326412, 691239, 1463829, 3099934, 6564695, 13901980, 29440065, 62344891, 132027067, 279592219, 592089264, 1253860704, 2655286560
(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 888
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FORMULA
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G.f.: (-1+x)*(-1+x^3)/(1-2*x-x^3+x^4)
Recurrence: {a(1)=1, a(0)=1, a(3)=4, a(2)=2, a(4)=9, a(n)-a(n+1)-2*a(n+3)+a(n+4)}
Sum(-1/643*(74*_alpha-53*_alpha^2+93*_alpha^3-168)*_alpha^(-1-n), _alpha=RootOf(1-2*_Z-_Z^3+_Z^4))
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MAPLE
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spec := [S, {S=Sequence(Prod(Sequence(Z), Sequence(Prod(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: A011955 A084172 A018100 this_sequence A036616 A136298 A122584
Adjacent sequences: A052905 A052906 A052907 this_sequence A052909 A052910 A052911
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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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