The distance to square-free polynomials

TL;DR

This paper investigates the proximity of integer polynomials to square-free polynomials, proving the existence of infinitely many such polynomials within a certain coefficient distance and establishing bounds on this distance.

Contribution

It demonstrates that any integer polynomial can be approximated by a square-free polynomial within a coefficient sum of 2, and constructs polynomials that cannot be approximated within 1.

Findings

Existence of infinitely many square-free polynomials within L(f-g) ≤ 2 for any polynomial f.

Construction of polynomials of degree ≥16 that are not close to any square-free polynomial within L(f-g) ≤ 1.

Analysis of polynomial distances to square-free polynomials over prime fields.

Abstract

In this paper, we consider a variant of Tur\'an's problem on the distance from an integer polynomial in $\mathbb{Z}[x]$ to the nea\-rest irreducible polynomial in $\mathbb{Z}[x]$. We prove that for any polynomial $f \in \mathbb{Z}[x]$, there exist infinitely many square-free polynomials $g\in \mathbb{Z}[x]$ such that $L(f-g) \le 2$, where $L(f-g)$ denotes the sum of the absolute values of the coefficients of $f-g$. On the other hand, we show that this inequality cannot be replaced by $L(f-g) \le 1$. For this, for each integer $d \geq 16$ we construct infinitely many polynomials $f \in \mathbb{Z}[x]$ of degree $d$ such that neither $f$ itself nor any $f(x) \pm x^k$, where $k$ is a non-negative integer, is square-free. Polynomials over prime fields and their distances to square-free polynomials are also considered.