A005678 A squarefree ternary sequence.

1, 2, 1, 3, 2, 1, 2, 3, 1, 2, 1, 3, 2, 3, 1, 3, 2, 1, 2, 3, 1, 2, 1, 3, 2, 1, 2, 3, 1, 3, 2, 3, 1, 2, 1, 3, 2, 1, 2, 3, 1, 2, 1, 3, 2, 3, 1, 3, 2, 1, 2, 3, 1, 3, 2, 3, 1, 2, 1, 3, 2, 3, 1, 3, 2, 1, 2, 3, 1, 2, 1, 3, 2, 1, 2, 3, 1, 3, 2, 3, 1, 2, 1, 3, 2, 1, 2

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Comments

Rules: 1 -> 1213, 2 -> 2123, 3 preceded by 1 -> 2313, 3 preceded by 2 -> 1323. - Sean A. Irvine, Nov 08 2020

References

• G. Siebert, personal communication.
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
• A. Thue. Über unendliche Zeichenreihen, Norske Vid. Selsk. Skr. I. Mat. Nat. Kl. Christiania, No. 7 (1906), 1-22. See p. 14.

Links

• J. Berstel, Axel Thue's papers on repetitions in words: a translation, 1994.
• David M. Cerna, A Note On Square-free Sequences and Anti-unification Type, arXiv:2412.10307 [cs.LO], 2024. See p. 4.
• G. Siebert, Letter to N. J. A. Sloane, Sept. 1977

Extensions

More terms from Sean A. Irvine, Nov 08 2020