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Search: id:A005656
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| A005656 |
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Number of bracelets (turn over necklaces) with n red, 1 pink and n-3 blue beads; also reversible strings with n red and n-3 blue beads.
(Formerly M2920)
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+0
1
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| 0, 0, 1, 3, 12, 44, 170, 651, 2520, 9752, 37854, 147070, 572264, 2229096, 8692788, 33933459, 132594480, 518584880, 2029976630, 7952706234, 31179618184, 122331419080, 480283635468, 1886828198398
(list; graph; listen)
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OFFSET
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1,4
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
Ascher, Marcia; Mu torere: an analysis of a Maori game. Math. Mag. 60 (1987), no. 2, 90-100.
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LINKS
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Index entries for sequences related to bracelets
F. Ruskey, Necklaces, Lyndon words, De Bruijn sequences, etc.
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FORMULA
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a(n)= (1/2) (C(2n-3, n-3)+C(n-2, [ (n-3)/2 ])).
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PROGRAM
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(PARI) a(n)= (1/2) *(C(2*n-3, n-3)+C(n-2, (n-3)\2)) where C(n, k)= if(k<0|k>n, 0, n!/k!/(n-k)!)
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CROSSREFS
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A005656(n)=A034851(2n-3, n-3)
Sequence in context: A012873 A167477 A109437 this_sequence A064017 A005320 A062561
Adjacent sequences: A005653 A005654 A005655 this_sequence A005657 A005658 A005659
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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Sequence corrected, extended and description corrected by Christian G. Bower (bowerc(AT)usa.net). Formula from Michael Somos.
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