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 A073057 Start with the word 1234, repeatedly append the words obtained via the maps 1 -> 12, 2 -> 13, 3 -> 42, 4 -> 43. 2
 1, 2, 3, 4, 1, 2, 1, 3, 4, 2, 4, 3, 1, 2, 1, 3, 4, 2, 4, 3, 1, 2, 1, 3, 1, 2, 4, 2, 4, 3, 1, 3, 4, 3, 4, 2, 1, 2, 1, 3, 4, 2, 4, 3, 1, 2, 1, 3, 1, 2, 4, 2, 4, 3, 1, 3, 4, 3, 4, 2, 1, 2, 1, 3, 1, 2, 4, 2, 4, 3, 1, 3, 4, 3, 4, 2, 1, 2, 1, 3, 1, 2, 4, 2, 1, 2, 1, 3, 4, 3, 1, 3, 4, 3, 4, 2, 1, 2, 4, 2, 4, 3, 4, 2, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Fixed point of the morphism 1 -> 12, 2 -> 13, 3 -> 42, 4 ->43, starting from a(1-4) = 1234. - Robert G. Wilson v, Apr 02 2009 [not quite correct, see name, Joerg Arndt, Feb 27 2018] LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..2900 J. P. Allouche, SchrÃ¶dinger operators with Rudin-Shapiro potentials are not palindromic, J. Math. Phys. 38 (1997), no. 4, 1843-1848. Scott Balchin and Dan Rust, Computations for Symbolic Substitutions, Journal of Integer Sequences, Vol. 20 (2017), Article 17.4.1. EXAMPLE The first step takes {1,2,3,4} to {1,2,3,4, 1,2, 1,3, 4,2, 4,3}. The next takes this to {1,2,3,4,1,2,1,3,4,2,4,3, 1,2, 1,3, 4,2, 4,3, 1,2, 1,3, 1,2, 4,2, 4,3, 1,3, 4,3, 4,2} MATHEMATICA Nest[ Flatten[ Join[ #, # /. {1 -> {1, 2}, 2 -> {1, 3}, 3 -> {4, 2}, 4 -> {4, 3}}]] &, {1, 2, 3, 4}, 3] (* Robert G. Wilson v, Apr 02 2009 *) CROSSREFS Cf. A020987, A073058. Sequence in context: A195451 A298160 A118310 * A084310 A214063 A078978 Adjacent sequences:  A073054 A073055 A073056 * A073058 A073059 A073060 KEYWORD nonn AUTHOR Roger L. Bagula, Aug 16 2002 EXTENSIONS New name using a (corrected) comment by Robert G. Wilson from Joerg Arndt, Feb 27 2018 STATUS approved

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Last modified March 26 01:08 EDT 2019. Contains 321479 sequences. (Running on oeis4.)