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 A056336 Number of primitive (aperiodic) reversible string structures with n beads using exactly two different colors. 1
 0, 1, 2, 4, 9, 16, 35, 66, 133, 261, 527, 1032, 2079, 4123, 8244, 16440, 32895, 65639, 131327, 262380, 524762, 1049071, 2098175, 4195230, 8390646, 16779231, 33558392, 67112892, 134225919, 268443306 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS A string and its reverse are considered to be equivalent. Permuting the colors will not change the structure. Identical to A056331 for n>1. REFERENCES M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia. [See A056391 for pdf file of Chap. 2] LINKS FORMULA a(n) = A056331(n) - A063524(n). MATHEMATICA a[1] = 0; a[n_] := DivisorSum[n, MoebiusMu[#] (2^(n/#-2) + 2^(Floor[n/#/2]-1))&]; Array[a, 30] (* Jean-François Alcover, Jun 29 2018 *) CROSSREFS Column 2 of A276544. Cf. A056318, A056331, A063524. Sequence in context: A005980 A128093 A056331 * A203318 A282776 A283015 Adjacent sequences:  A056333 A056334 A056335 * A056337 A056338 A056339 KEYWORD nonn AUTHOR STATUS approved

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Last modified May 15 10:54 EDT 2021. Contains 343909 sequences. (Running on oeis4.)