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Search: id:A032280
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| A032280 |
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Number of bracelets (turn over necklaces) of n beads of 2 colors, 7 of them black. |
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3
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| 1, 1, 4, 8, 20, 38, 76, 133, 232, 375, 600, 912, 1368, 1980, 2829, 3936, 5412, 7293, 9724, 12760, 16588, 21287, 27092, 34112, 42640, 52819, 65008, 79392, 96405, 116280, 139536, 166464, 197676, 233529, 274740, 321741, 375364
(list; graph; listen)
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OFFSET
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7,3
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REFERENCES
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S. J. Cyvin et al., Polygonal systems including the corannulene ... homologs ..., Z. Naturforsch., 52a (1997), 867-873.
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LINKS
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C. G. Bower, Transforms (2)
F. Ruskey, Necklaces, Lyndon words, De Bruijn sequences, etc.
Index entries for sequences related to bracelets
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FORMULA
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S. J. Cyvin et al. give a g.f.
"DIK[ 7 ]" (necklace, indistinct, unlabeled, 7 parts) transform of 1, 1, 1, 1...
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MATHEMATICA
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k = 7; Table[(Apply[Plus, Map[EulerPhi[ # ]Binomial[n/#, k/# ] &, Divisors[GCD[n, k]]]]/n + Binomial[If[OddQ[n], n - 1, n - If[OddQ[k], 2, 0]]/2, If[OddQ[k], k - 1, k]/2])/2, {n, k, 50}] - Robert A. Russell (russell(AT)post.harvard.edu), Sep 27 2004
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CROSSREFS
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Sequence in context: A097164 A133628 A097940 this_sequence A156303 A008136 A047196
Adjacent sequences: A032277 A032278 A032279 this_sequence A032281 A032282 A032283
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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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