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Search: id:A054480
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| A054480 |
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Number of different positive braids with n crossings of 4 strands. |
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+0
2
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| 1, 3, 8, 19, 43, 94, 202, 429, 905, 1901, 3983, 8332, 17413, 36370, 75938, 158519, 330862, 690523, 1441082, 3007369, 6275917, 13096737, 27330418, 57033206, 119016808, 248363751, 518283950, 1081551220, 2256972626, 4709831964
(list; graph; listen)
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OFFSET
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0,2
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REFERENCES
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P. Xu, Growth of the positive braids semigroups, Journal of Pure and Applied Algebra, 1992.
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FORMULA
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G.f.: 1/(1-3x+x^2+2x^3-x^6)
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EXAMPLE
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a(3)=19 =#{111,112,113,121,122,123,132,133,211,213,221,222,223,232,233,321,322,332,333}
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CROSSREFS
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Cf. A000071, A054761.
Sequence in context: A161993 A008466 A102712 this_sequence A121551 A077850 A097550
Adjacent sequences: A054477 A054478 A054479 this_sequence A054481 A054482 A054483
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KEYWORD
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nonn,easy
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AUTHOR
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Serge Burckel (burckel(AT)univ-reunion.fr), Apr 26 2000
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EXTENSIONS
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More terms from Benoit Cloitre (benoit7848c(AT)orange.fr), Mar 22 2002
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