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A056328
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Number of reversible string structures with n beads using exactly four different colors.
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0
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0, 0, 0, 1, 6, 37, 183, 877, 3930, 17185, 73095, 306361, 1267266, 5198557, 21182343, 85910917, 347187210, 1399451545, 5629911015, 22616256721, 90754855026, 363890126677, 1458172596903, 5840531635357, 23385650196090
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,5
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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
| A056323(n)-A001998(n-1).
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CROSSREFS
| Cf. A056311.
Sequence in context: A047670 A129552 A056338 * A156185 A057418 A001419
Adjacent sequences: A056325 A056326 A056327 * A056329 A056330 A056331
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KEYWORD
| nonn
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AUTHOR
| Marks R. Nester (nesterm(AT)dpi.qld.gov.au)
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