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A125047
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Infinite word generated by mapping 1->12, 2->13, 3->43, 4->42 starting at 1.
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0
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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; internal format)
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OFFSET
| 1,2
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COMMENTS
| Infinite word over 4-letter alphabet that contains no squares in arithmetic progressions of odd difference. - Ralf Stephan, May 09 2007
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LINKS
| J.-Y. Kao et al., Words avoiding repetitions in arithmetic progressions
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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
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EXAMPLE
| 1 -> 12 -> 1213 -> 12131242 -> 1213124312134243 -> ...
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PROG
| (PARI) {a(n)=local(A); if(n<1, 0, A=[1]; while(length(A)<n, A=concat(vector(length(A), k, [[1, 2], [1, 3], [4, 3], [4, 2]][A[k]]))); A[n])}
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CROSSREFS
| Cf. A038190.
Sequence in context: A056951 A130212 A133737 * A045898 A036262 A169613
Adjacent sequences: A125044 A125045 A125046 * A125048 A125049 A125050
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KEYWORD
| nonn
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AUTHOR
| Michael Somos, Nov 17 2006
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