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 A003324 A nonrepetitive sequence. (Formerly M0443) 1
 1, 2, 3, 4, 1, 4, 3, 2, 1, 2, 3, 2, 1, 4, 3, 4, 1, 2, 3, 4, 1, 4, 3, 4, 1, 2, 3, 2, 1, 4, 3, 2, 1, 2, 3, 4, 1, 4, 3, 2, 1, 2, 3, 2, 1, 4, 3, 2, 1, 2, 3, 4, 1, 4, 3, 4, 1, 2, 3, 2, 1, 4, 3, 4, 1, 2, 3, 4, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Let b(0) be the sequence 1,2,3,4. Proceeding by induction, let b(n) be a sequence of length 2^(n+2). Quarter b(n) into four blocks, A,B,C,D each of length 2^n, so that b(n) = ABCD. Then b(n+1) = ABCDADCB. [After Dean paper.] - Sean A. Irvine, Apr 20 2015 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Sean A. Irvine, Table of n, a(n) for n = 1..10000 Richard A. Dean, A sequence without repeats on x, x^{-1}, y, y^{-1}, Amer. Math. Monthly 72, 1965. pp. 383-385. MR 31 #350. Françoise Dejean, Sur un Theoreme de Thue, J. Combinatorial Theory, vol. 13 A, iss. 1 (1972) 90-99. N. J. A. Sloane, P. Flor, L. F. Meyers, G. A. Hedlund. M. Gardner, Collection of documents and notes related to A1285, A3270, A3324 MATHEMATICA b[0] = Range[4]; b[n_] := b[n] = Module[{aa, bb, cc, dd}, {aa, bb, cc, dd} = Partition[b[n - 1], 2^(n-1)]; Join[aa, bb, cc, dd, aa, dd, cc, bb] // Flatten]; b[5] (* Jean-François Alcover, Sep 27 2017 *) CROSSREFS Sequence in context: A270313 A327464 A318308 * A110630 A238883 A325242 Adjacent sequences:  A003321 A003322 A003323 * A003325 A003326 A003327 KEYWORD nonn,nice AUTHOR STATUS approved

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Last modified February 20 14:03 EST 2020. Contains 332078 sequences. (Running on oeis4.)