English

Fermat's and Catalan's equations over $M_2(\mathbb{Z})$

Number Theory 2025-03-06 v1

Abstract

Let A=(abcd)M2(Z)A=\begin{pmatrix} a & b \\ c & d \end{pmatrix}\in M_2\left(\mathbb{Z}\right) be a given matrix such that bc0bc\neq0 and let C(A)={BM2(Z):AB=BA}C(A)=\{B\in M_2(\mathbb{Z}): AB=BA\}. In this paper, we give a necessary and sufficient condition for the solvability of the matrix equation uXi+vYj=wZk,i,j,kN,X,Y,ZC(A)uX^i+vY^j=wZ^k,\, i,\, j,\, k\in\mathbb{N},\, X, \,Y,\, Z\in C(A), where u,v,wu,\, v,\, w are given nonzero integers such that gcd(u,v,w)=1\gcd\left(u,\, v,\, w\right)=1. From this, we get a necessary and sufficient condition for the solvability of the Fermat's matrix equation in C(A)C(A). Moreover, we show that the solvability of the Catalan's matrix equation in M2(Z)M_2\left(\mathbb{Z}\right) can be reduced to the solvability of the Catalan's matrix equation in C(A)C(A), and finally to the solvability of the Catalan's equation in quadratic fields.

Keywords

Cite

@article{arxiv.2503.03621,
  title  = {Fermat's and Catalan's equations over $M_2(\mathbb{Z})$},
  author = {Hongjian Li and Pingzhi Yuan},
  journal= {arXiv preprint arXiv:2503.03621},
  year   = {2025}
}