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arXiv · 2006.06837

Stuttering Conway Sequences Are Still Conway Sequences

Éric Brier·Rémi Géraud-Stewart·David Naccache·Alessandro Pacco·Emanuele Troiani
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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 $d \neq 1$ gives Conway's sequence: $d$, $1d$, $111d$, $311d$, $13211d$, 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 $1, 2, 4, 6, d$, where $d$ 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.

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Éric Brier, Rémi Géraud-Stewart, David Naccache, Alessandro Pacco, Emanuele Troiani. 2020-06-11. Stuttering Conway Sequences Are Still Conway Sequences. https://arxiv.org/abs/2006.06837

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