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 A125047 Infinite word generated by mapping 1->12, 2->13, 3->43, 4->42 starting at 1. 2
 1, 2, 1, 3, 1, 2, 4, 3, 1, 2, 1, 3, 4, 2, 4, 3, 1, 2, 1, 3, 1, 2, 4, 3, 4, 2, 1, 3, 4, 2, 4, 3, 1, 2, 1, 3, 1, 2, 4, 3, 1, 2, 1, 3, 4, 2, 4, 3, 4, 2, 1, 3, 1, 2, 4, 3, 4, 2, 1, 3, 4, 2, 4, 3, 1, 2, 1, 3, 1, 2, 4, 3, 1, 2, 1, 3, 4, 2, 4, 3, 1, 2, 1, 3, 1, 2, 4, 3, 4, 2, 1, 3, 4, 2, 4, 3, 4, 2, 1, 3, 1, 2, 4, 3, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Infinite word over 4-letter alphabet that contains no squares in arithmetic progressions of odd difference. - Ralf Stephan, May 09 2007 LINKS Table of n, a(n) for n=1..105. Jui-Yi Kao, Narad Rampersad, Jeffrey Shallit, Manuel Silva, Words avoiding repetitions in arithmetic progressions, Theoretical Computer Science, volume 391, issues 1-2, February 2008, pages 126-137.  And arXiv:math/0608607 [math.CO], 2006. Index entries for sequences that are fixed points of mappings FORMULA Recurrence: a(1)=1, a(4n)=3, a(4n+2)=2, a(8n+3)=1, a(8n+7)=4, a(4n+1)=a(2n+1). - Ralf Stephan, May 09 2007 EXAMPLE 1 -> 12 -> 1213 -> 12131242 -> 1213124312134243 -> ... MATHEMATICA SubstitutionSystem[{1 -> {1, 2}, 2 -> {1, 3}, 3 -> {4, 3}, 4 -> {4, 2}}, {1}, 7] // Last (* Jean-François Alcover, Dec 17 2018 *) PROG (PARI) {a(n)=local(A); if(n<1, 0, A=[1]; while(length(A) 1023), A122002 (map 1234 -> 5137). Cf. A038190. Sequence in context: A213361 A212121 A213371 * A323420 A331296 A270656 Adjacent sequences: A125044 A125045 A125046 * A125048 A125049 A125050 KEYWORD nonn AUTHOR Michael Somos, Nov 17 2006 STATUS approved

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Last modified June 2 07:25 EDT 2023. Contains 363081 sequences. (Running on oeis4.)