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arXiv · 2401.09497

Weakly Consecutive Sequences

Thomas Garrison·Chris Seiler·Andrew Knowles
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Abstract

A weakly consecutive sequence (WCS) is a permutation $\sigma$ of $\{1, \ldots, k\}$ such that if an integer $d$ divides $\sigma(i)$, then $d$ also divides $\sigma(i \pm d)$ insofar as these are defined. The structure of weakly consecutive sequences is surprisingly rich, and it is difficult to find a formula for the number $N(k)$ of WCS's of length $k$. However, for a given $k$ we describe four starting sequences, to each of which we can apply three \emph{rules} or operations to generate new WCS's. We conjecture that any WCS can be constructed by applying these rules, which depend in an intricate way on the primality of $k$ and surrounding integers. We find bounds for $N(k)$ by analyzing these rules.

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Thomas Garrison, Chris Seiler, Andrew Knowles. 2024-01-17. Weakly Consecutive Sequences. https://arxiv.org/abs/2401.09497

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