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Search: id:A056323
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| A056323 |
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Number of reversible string structures with n beads using a maximum of four different colors. |
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+0
4
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| 1, 2, 4, 11, 31, 107, 379, 1451, 5611, 22187, 87979, 350891, 1400491, 5597867, 22379179, 89500331, 357952171, 1431743147, 5726775979, 22906841771, 91626580651, 366505274027, 1466017950379, 5864067607211
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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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
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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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FORMULA
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Use de Bruijn's generalization of Polya's enumeration theorem as discussed in reference.
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CROSSREFS
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Cf. A032121.
Sequence in context: A148169 A110140 A115625 this_sequence A081557 A154603 A063254
Adjacent sequences: A056320 A056321 A056322 this_sequence A056324 A056325 A056326
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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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