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A056329
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Number of reversible string structures with n beads using exactly five different colors.
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0
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0, 0, 0, 0, 1, 9, 76, 542, 3523, 21393, 123680, 690550, 3756151, 20042589, 105394296, 548123982, 2826435403, 14479204833, 73794961960, 374603884910, 1895632969351, 9568915372269, 48208452866816
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OFFSET
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1,6
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COMMENTS
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A string and its reverse are considered to be equivalent. Permuting the colors will not change the structure.
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REFERENCES
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M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia.
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LINKS
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Table of n, a(n) for n=1..23.
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FORMULA
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a(n) = A056324(n)-A056323(n).
Empirical G.f.: -x^5*(70*x^5-102*x^4+22*x^3+7*x^2-4*x+1) / ((x-1)*(2*x-1)*(2*x+1)*(3*x-1)*(4*x-1)*(5*x-1)*(2*x^2-1)*(5*x^2-1)). [Colin Barker, Nov 25 2012]
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CROSSREFS
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Cf. A056312.
Sequence in context: A161736 A226180 A056339 * A190982 A082677 A185818
Adjacent sequences: A056326 A056327 A056328 * A056330 A056331 A056332
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KEYWORD
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nonn
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AUTHOR
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Marks R. Nester (nesterm(AT)dpi.qld.gov.au)
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STATUS
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approved
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