English

Stuttering Conway Sequences Are Still Conway Sequences

Dynamical Systems 2020-06-15 v1 Formal Languages and Automata Theory Combinatorics

Abstract

A look-and-say sequence is obtained iteratively by reading off the digits of the current value, grouping identical digits together: starting with 1, the sequence reads: 1, 11, 21, 1211, 111221, 312211, etc. (OEIS A005150). Starting with any digit d1d \neq 1 gives Conway's sequence: dd, 1d1d, 111d111d, 311d311d, 13211d13211d, etc. (OEIS A006715). Conway popularised these sequences and studied some of their properties. In this paper we consider a variant subbed "look-and-say again" where digits are repeated twice. We prove that the look-and-say again sequence contains only the digits 1,2,4,6,d1, 2, 4, 6, d, where dd represents the starting digit. Such sequences decompose and the ratio of successive lengths converges to Conway's constant. In fact, these properties result from a commuting diagram between look-and-say again sequences and "classical" look-and-say sequences. Similar results apply to the "look-and-say three times" sequence.

Keywords

Cite

@article{arxiv.2006.06837,
  title  = {Stuttering Conway Sequences Are Still Conway Sequences},
  author = {Éric Brier and Rémi Géraud-Stewart and David Naccache and Alessandro Pacco and Emanuele Troiani},
  journal= {arXiv preprint arXiv:2006.06837},
  year   = {2020}
}
R2 v1 2026-06-23T16:15:28.424Z