English

Quadratic residues and related permutations

Number Theory 2025-03-04 v4

Abstract

Let pp be an odd prime. For any pp-adic integer aa we let a\overline{a} denote the unique integer xx with p/2<x<p/2-p/2<x<p/2 and xax-a divisible by pp. In this paper we study some permutations involving quadratic residues modulo pp. For instance, we consider the following three sequences. \begin{align*} &A_0: \overline{1^2},\ \overline{2^2},\ \cdots,\ \overline{((p-1)/2)^2},\\ &A_1: \overline{a_1},\ \overline{a_2},\ \cdots,\ \overline{a_{(p-1)/2}},\\ &A_2: \overline{g^2},\ \overline{g^4},\ \cdots,\ \overline{g^{p-1}}, \end{align*} where gZg\in\Z is a primitive root modulo pp and 1a1<a2<<a(p1)/2p11\le a_1<a_2<\cdots<a_{(p-1)/2}\le p-1 are all quadratic residues modulo pp. Obviously AiA_i is a permutation of AjA_j and we call this permutation σi,j\sigma_{i,j}. Sun obtained the sign of σ0,1\sigma_{0,1} when p3(mod4)p\equiv 3\pmod4. In this paper we give the sign of σ0,1\sigma_{0,1} and determine the sign σ0,2\sigma_{0,2} when p1(mod4)p\equiv 1\pmod 4.

Keywords

Cite

@article{arxiv.1903.01098,
  title  = {Quadratic residues and related permutations},
  author = {Hai-Liang Wu},
  journal= {arXiv preprint arXiv:1903.01098},
  year   = {2025}
}
R2 v1 2026-06-23T07:57:08.903Z