id:A056327 - OEIS Search Results

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Number of reversible string structures with n beads using exactly three different colors.

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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; listen)

	OFFSET	`1,4`
	COMMENT	`A string and its reverse are considered to be equivalent. Permuting the colors will not change the structure.`
	REFERENCES	`M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia.`
	FORMULA	`A001998(n-1)-A005418(n).`
	CROSSREFS	`Cf. A056310.` `Sequence in context: A143215 A132308 A026110 this_sequence A026328 A014532 A094705` `Adjacent sequences: A056324 A056325 A056326 this_sequence A056328 A056329 A056330`
	KEYWORD	`nonn`
	AUTHOR	`Marks R. Nester (nesterm(AT)dpi.qld.gov.au)`

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Last modified December 20 00:58 EST 2009. Contains 171054 sequences.

AT&T Labs Research