Journal of Integer Sequences, Vol. 29 (2026), Article 26.4.1

Meta-Automatic Sequences


John M. Campbell
Department of Mathematics and Statistics
Dalhousie University
Halifax, NS B3H 4R2
Canada

Benoît Cloitre
19, rue Louise Michel
92300 Levallois-Perret
France

Abstract:

Nested (or meta-Fibonacci) recurrences, such as the recurrence used to define Hofstadter's Q-sequence, along with the digit-based recurrences that underlie automatic sequences are of interest from both number-theoretic and combinatorial points of view. In this direction, Allouche and Shallit showed how the frequency sequence of a variant of the Q-sequence is 2-automatic. This inspires us to introduce what may be seen as a natural combination of the recurrences for meta-Fibonacci and automatic sequences, by introducing the concept of a meta-automatic sequence. We exhibit two binary meta-automatic sequences ℳ1 and ℳ2 whose defining recurrences do not satisfy the Allouche-Shallit automaticity criterion directly, and this is formalized in our paper. For each of these integer sequences ℳ1 and ℳ2, we prove explicit DFAO evaluations, together with 4-uniform morphisms, and we also consider the factor complexities of these sequences.


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(Concerned with sequences A005185 A039982 A244477 A298952 A391614 A392736.)


Received March 2 2026; revised version received May 26 2026. Published in Journal of Integer Sequences, June 4 2026.


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