English

Finite beta-expansions of natural numbers

Number Theory 2025-09-23 v1

Abstract

Let β>1\beta>1. For x[0,)x \in [0,\infty), we have so-called the β\beta-expansion of xx in base β\beta as follows: x=jkxjβj=xkβk++x1β+x0+x1β1+x2β2+x= \sum_{j \leq k} x_{j}\beta^{j} = x_{k}\beta^{k}+ \cdots + x_{1}\beta+x_{0}+x_{-1}\beta^{-1} + x_{-2}\beta^{-2} + \cdots where kZk \in \mathbb{Z}, βkx<βk+1\beta^{k} \leq x < \beta^{k+1}, xjZ[0,β)x_{j} \in \mathbb{Z} \cap [0,\beta) for all jkj \leq k and jnxjβj<βn+1\sum_{j \leq n}x_{j}\beta^{j}<\beta^{n+1} for all nkn \leq k. In this paper, we give a sufficient condition (for β\beta) such that each element of N\mathbb{N} has the finite beta-expansion in base β\beta. Moreover we also find a β\beta with this finiteness property which does not have positive finiteness property.

Keywords

Cite

@article{arxiv.2306.01770,
  title  = {Finite beta-expansions of natural numbers},
  author = {Fumichika Takamizo},
  journal= {arXiv preprint arXiv:2306.01770},
  year   = {2025}
}