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Search: id:A032123
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| A032123 |
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Number of 2n-bead black-white reversible strings with n black beads. |
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+0
2
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| 1, 1, 4, 10, 38, 126, 472, 1716, 6470, 24310, 92504, 352716, 1352540, 5200300, 20060016, 77558760, 300546630, 1166803110, 4537591960, 17672631900, 68923356788, 269128937220, 1052049834576, 4116715363800
(list; graph; listen)
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OFFSET
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0,3
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LINKS
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C. G. Bower, Transforms (2)
N. J. A. Sloane, Classic Sequences
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FORMULA
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n odd: C(2n-1, n-1); n even: C(2n-1, n-1) + C(n-1, n/2-1)
"BIK[ n ](2n-1)" (reversible, indistinct, unlabeled, n parts, 2n-1 elements) transform of 1, 1, 1, 1...
E.g.f.: exp(x)*cosh(x)*BesselI(0, 2*x). - Vladeta Jovovic (vladeta(AT)eunet.rs), Apr 07 2005
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CROSSREFS
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Central column of Losanitsch's triangle A034851.
Sequence in context: A046562 A149191 A149192 this_sequence A149193 A149194 A149195
Adjacent sequences: A032120 A032121 A032122 this_sequence A032124 A032125 A032126
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KEYWORD
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nonn
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AUTHOR
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Christian G. Bower (bowerc(AT)usa.net)
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