English

Binary sequences meet the Fibonacci sequence

Number Theory 2025-05-14 v2

Abstract

We introduce a new family of meta-Fibonacci sequences (f(n))nN(f(n))_{n\in\mathbb{N}}, governed by the recurrence relation f(n)=af(nun1)+bf(nun2),f(n)=af(n-u_{n}-1)+bf(n-u_{n}-2), where u=(un)nN\mathbf{u}=(u_{n})_{n\in \mathbb{N}} is a sequence with values 0,10,1. Our study focuses on the properties of the sequence of quotients h(n)=f(n+1)/f(n)h(n) = f(n+1)/f(n) and its set of values V(f)={h(n):nN}\mathcal{V}(f)=\{h(n): n \in \mathbb{N}\} for various u\mathbf{u}. We give a sufficient condition for finiteness of V(f)\mathcal{V}(f) and automaticity of (h(n))nN(h(n))_{n \in \mathbb{N}}, which holds in particular when u\mathbf{u} is the famous Prouhet-Thue-Morse sequence. In the automatic case, a constructive approach is used, with the help of the software \texttt{Walnut}. On the other hand, we prove that the set V(f)\cal{V}(f) is infinite for other special binary sequences u\mathbf{u}, and obtain a trichotomy in its topological type when u\mathbf{u} is eventually periodic.

Keywords

Cite

@article{arxiv.2412.11319,
  title  = {Binary sequences meet the Fibonacci sequence},
  author = {Piotr Miska and Bartosz Sobolewski and Maciej Ulas},
  journal= {arXiv preprint arXiv:2412.11319},
  year   = {2025}
}

Comments

20 pages, 3 figures

R2 v1 2026-06-28T20:36:02.451Z