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A056327
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Number of reversible string structures with n beads using exactly three different colors.
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0
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0, 0, 1, 4, 15, 50, 160, 502, 1545, 4730, 14356, 43474, 131145, 395150, 1188580, 3572902, 10732065, 32225810, 96733636, 290322394, 871200825, 2614097750, 7843255300, 23531775502, 70599259185, 211805902490
(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. Permuting the colors will not change the structure.
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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
| A001998(n-1)-A005418(n).
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CROSSREFS
| Cf. A056310.
Sequence in context: A143215 A132308 A026110 * A026328 A014532 A094705
Adjacent sequences: A056324 A056325 A056326 * A056328 A056329 A056330
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KEYWORD
| nonn
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AUTHOR
| Marks R. Nester (nesterm(AT)dpi.qld.gov.au)
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