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A006840
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Number of 2n-bead black-white reversible complementable necklaces with n black beads.
(Formerly M0837)
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6
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1, 1, 2, 3, 7, 13, 35, 85, 257, 765, 2518, 8359, 28968, 101340, 361270, 1297879, 4707969, 17179435, 63068876, 232615771, 861725794, 3204236779, 11955836258, 44748176653, 167959144032, 632058070310, 2384235077576, 9013628451275
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OFFSET
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0,3
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REFERENCES
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J. A. Hoskins, C. E. Praeger and A. P. Street, Balanced twills with bounded float length, Congress. Numerantium, 40 (1983), 77-89.
W. D. Hoskins; Anne Penfold Street, Twills on a given number of harnesses, J. Austral. Math. Soc. Ser. A 33 (1982), no. 1, 1-15.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Table of n, a(n) for n=0..27.
Index entries for sequences related to bracelets
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FORMULA
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If n is odd, 1/2 (A045629 + 1/2 C(n-1, (n-1)/2) + 2^(n-2)); if n is even, 1/2 (A045629 + 1/2 C(n, n/2) + 2^(n-2)) (Christian Bower).
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CROSSREFS
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Sequence in context: A129859 A056953 A045611 * A123408 A033995 A013917
Adjacent sequences: A006837 A006838 A006839 * A006841 A006842 A006843
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane.
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EXTENSIONS
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More terms from David W. Wilson.
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STATUS
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approved
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