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A056311
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Number of reversible strings with n beads using exactly four different colors.
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2
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0, 0, 0, 12, 120, 780, 4212, 20424, 93360, 409380, 1749780, 7338792, 30394560, 124705140, 508291812, 2061607224, 8332140720, 33585777060, 135116412660, 542785800072, 2178110589600, 8733345234900
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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COMMENTS
| A string and its reverse are considered to be equivalent.
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REFERENCES
| M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia.
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FORMULA
| Equals A032121(n)-4*A032120(n)+6*A005418(n+1)-4.
G.f.: 12*x^4*(3*x+1)*(8*x^4-3*x^3-2*x^2-x+1)/ ((x-1) * (4*x-1) * (3*x-1) * (2*x+1) * (2*x -1) * (3*x^2-1) * (2*x^2-1)) [From Maksym Voznyy (voznyy(AT)mail.ru), Jul 27 2009] [Corrected by R. J. Mathar, Sep 16 2009]
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CROSSREFS
| Cf. A032121.
Sequence in context: A001816 A133386 A056320 * A009050 A067358 A061506
Adjacent sequences: A056308 A056309 A056310 * A056312 A056313 A056314
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KEYWORD
| nonn
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AUTHOR
| Marks R. Nester (nesterm(AT)dpi.qld.gov.au)
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EXTENSIONS
| G.f. proposed by Maksym Voznyy checked and corrected by R. J. Mathar, Sep 16 2009.
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