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A032094
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Number of reversible strings with n-1 beads of 2 colors. 7 beads are black. String is not palindromic.
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4
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4, 16, 60, 160, 396, 848, 1716, 3200, 5720, 9696, 15912, 25152, 38760, 58080, 85272, 122496, 173052, 240240, 328900, 443872, 592020, 780208, 1017900, 1314560, 1682928, 2135744, 2689808, 3361920, 4173840, 5147328, 6310128
(list; graph; refs; listen; history; internal format)
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OFFSET
| 9,1
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COMMENTS
| If the offset is changed to 3, this is the 2nd Witt transform of A000292 [Moree]. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 08 2008]
Also 7-th column of A159916, i.e. number of 7-element subsets of {1,...,n-1} whose elements add up to an odd integer. [From M. F. Hasler (www.univ-ag.fr/~mhasler), May 02 2009]
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LINKS
| C. G. Bower, Transforms (2)
Pieter Moree, The formal series Witt transform, Discr. Math. no. 295 vol. 1-3 (2005) 143-160. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 08 2008]
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FORMULA
| "BHK[ 8 ]" (reversible, identity, unlabeled, 8 parts) transform of 1, 1, 1, 1...
G.f.: 4*x^9*(1+x^2)/((1-x)^8*(1+x)^4). a(n)=4*A031164(n-9). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 08 2008]
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PROG
| (PARI) A032094(n)=(binomial(n--, 7)-if(n%2, binomial(n\2, 3)))\2 [From M. F. Hasler (www.univ-ag.fr/~mhasler), May 02 2009]
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CROSSREFS
| Cf. A032091, A005995, A018210, A159916. [From M. F. Hasler (www.univ-ag.fr/~mhasler), May 02 2009]
Sequence in context: A123893 A134762 A047123 * A055295 A121254 A119827
Adjacent sequences: A032091 A032092 A032093 * A032095 A032096 A032097
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KEYWORD
| nonn
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AUTHOR
| Christian G. Bower (bowerc(AT)usa.net)
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