Blocking Sets and Power Residue Modulo Integers with Bounded Number of Prime Factors

Fuente: arXiv
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Autores principales: Mishra, Bhawesh, Santonastaso, Paolo
Formato: Preprint
Publicado: 2025
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author Mishra, Bhawesh
Santonastaso, Paolo
author_facet Mishra, Bhawesh
Santonastaso, Paolo
contents Let $q$ be an odd prime and $k$ be a natural number. We show that a finite subset of integers $S$ that does not contain any perfect $q^{th}$ power, contains a $q^{th}$ power residue modulo almost every natural numbers $N$ with at most $k$ prime factors if and only if $S$ corresponds to a $k$-blocking set of $\PG(\mathbb{F}_{q}^{n})$. Here, $n$ is the number of distinct primes that divides the $q$-free parts of elements of $S$. Consequently, this geometric connection enables us to utilize methods from Galois geometry to derive lower bounds for the cardinalities of such sets $S$ and to completely characterize such $S$ of the smallest and the second smallest cardinalities. Furthermore, the property of whether a finite subset of integers contains a $q^{th}$ power residue modulo almost every integer $N$ with at most $k$ prime factors is invariant under the action of projective general linear group $\mathrm{PGL}(n, q)$.
format Preprint
id arxiv_https___arxiv_org_abs_2507_11828
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Blocking Sets and Power Residue Modulo Integers with Bounded Number of Prime Factors
Mishra, Bhawesh
Santonastaso, Paolo
Number Theory
11A15, 51E21
Let $q$ be an odd prime and $k$ be a natural number. We show that a finite subset of integers $S$ that does not contain any perfect $q^{th}$ power, contains a $q^{th}$ power residue modulo almost every natural numbers $N$ with at most $k$ prime factors if and only if $S$ corresponds to a $k$-blocking set of $\PG(\mathbb{F}_{q}^{n})$. Here, $n$ is the number of distinct primes that divides the $q$-free parts of elements of $S$. Consequently, this geometric connection enables us to utilize methods from Galois geometry to derive lower bounds for the cardinalities of such sets $S$ and to completely characterize such $S$ of the smallest and the second smallest cardinalities. Furthermore, the property of whether a finite subset of integers contains a $q^{th}$ power residue modulo almost every integer $N$ with at most $k$ prime factors is invariant under the action of projective general linear group $\mathrm{PGL}(n, q)$.
title Blocking Sets and Power Residue Modulo Integers with Bounded Number of Prime Factors
topic Number Theory
11A15, 51E21
url https://arxiv.org/abs/2507.11828