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 A005679 A squarefree (or Thue-Morse) ternary sequence: closed under a->abc, b->ac, c->b. (Formerly M0140) 4
 2, 1, 3, 2, 3, 1, 2, 1, 3, 1, 2, 3, 2, 1, 3, 2, 3, 1, 2, 3, 2, 1, 3, 1, 2, 1, 3, 2, 3, 1, 2, 1, 3, 1, 2, 3, 2, 1, 3, 1, 2, 1, 3, 2, 3, 1, 2, 3, 2, 1, 3, 2, 3, 1, 2, 1, 3, 1, 2, 3, 2, 1, 3, 2, 3, 1, 2, 3, 2, 1, 3, 1, 2, 1, 3, 2, 3, 1, 2, 3, 2, 1, 3, 2, 3, 1, 2, 1, 3, 1, 2, 3, 2, 1, 3, 1, 2, 1, 3, 2, 3, 1, 2, 1, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Trajectory of 2 under the morphism 1 -> 23, 2 -> 213 & 3 -> 1. - Robert G. Wilson v, Apr 06 2008 Replace all 4's in A005681 by 1's and you get this sequence. - Sean A. Irvine, Aug 04 2016 REFERENCES A. Salomaa, Jewels of Formal Language Theory. Computer Science Press, Rockville, MD, 1981, p. 10. G. Siebert, personal communication. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Marston Morse and Gustav A. Hedlund, Unending chess, symbolic dynamics and a problem in semigroups, Duke Math. J., Volume 11, Number 1 (1944), 1-7. G. Siebert, Letter to N. J. A. Sloane, Sept. 1977 MATHEMATICA Nest[ # /. {1 -> {2, 3}, 2 -> {2, 1, 3}, 3 -> 1} &, {2}, 7] // Flatten (* Robert G. Wilson v, Apr 06 2008 *) CROSSREFS Cf. A005681. Sequence in context: A048233 A287730 A260452 * A232927 A275832 A237839 Adjacent sequences:  A005676 A005677 A005678 * A005680 A005681 A005682 KEYWORD nonn,easy,nice AUTHOR EXTENSIONS More terms from Robert G. Wilson v, Apr 06 2008 STATUS approved

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