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A056325
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Number of reversible string structures with n beads using a maximum of six different colors.
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3
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1, 2, 4, 11, 32, 117, 467, 2135, 10480, 55091, 301633, 1704115, 9819216, 57365191, 338134521, 2005134639, 11937364184, 71254895955, 426063226937, 2550552314219, 15280103807200, 91588104196415
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| A string and its reverse are considered to be equivalent. Permuting the colors will not change the structure. Thus aabc, cbaa and bbac are all considered to be identical.
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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
| Use de Bruijn's generalization of Polya's enumeration theorem as discussed in reference.
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CROSSREFS
| Cf. A056308.
Sequence in context: A113774 A124504 A056324 * A103293 A123418 A123412
Adjacent sequences: A056322 A056323 A056324 * A056326 A056327 A056328
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KEYWORD
| nonn
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AUTHOR
| Marks R. Nester (nesterm(AT)dpi.qld.gov.au)
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