English

Brik's sequence: a strange recursion

Combinatorics 2026-05-11 v1 Discrete Mathematics Formal Languages and Automata Theory Number Theory

Abstract

We study the properties of the sequence of words (Bi)(B_i), where B1=101B_1 = 101 and Bi+1=BiCiB_{i+1} = B_i C_i for i1i \geq 1, where CiC_i is BiB_i with the first ii symbols removed, and the infinite binary sequence b=10101101011011101{\bf b} = 10101101011011101 \cdots of which all the BiB_i are prefixes. We show that b\bf b is recurrent, but not uniformly recurrent; it has exponential factor complexity; it is not morphic; and the density of 11's exists and is transcendental.

Keywords

Cite

@article{arxiv.2605.07542,
  title  = {Brik's sequence: a strange recursion},
  author = {Jeffrey Shallit},
  journal= {arXiv preprint arXiv:2605.07542},
  year   = {2026}
}