Enumeration and decidable properties of automatic sequences

  • Authors:
  • Émilie Charlier;Narad Rampersad;Jeffrey Shallit

  • Affiliations:
  • University of Waterloo, Waterloo, ON, Canada;Department of Mathematics, University of Liège, Liège, Belgium;University of Waterloo, Waterloo, ON, Canada

  • Venue:
  • DLT'11 Proceedings of the 15th international conference on Developments in language theory
  • Year:
  • 2011

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Abstract

We show that various aspects of k-automatic sequences -- such as having an unbordered factor of length n -- are both decidable and effectively enumerable. As a consequence it follows that many related sequences are either k-automatic or k-regular. These include many sequences previously studied in the literature, such as the recurrence function, the appearance function, and the repetitivity index. We also give a new characterization of the class of k-regular sequences. Many results extend to other sequences defined in terms of Pisot numeration systems.