Decide whether for every polynomial $P$ of degree at least $1$, there exist infinitely many primes that divide $P(n)$ for at least one positive integer $n$. (Walther Janous)
Problem
Source: 2022 Austrian Federal Competition For Advanced Students, Part 2 p4
Tags: number theory, Integer Polynomial, polynomial
23.10.2022 19:20
In my opinion, a better translation would be: Decide whether for every polynomial P of degree at least 1, there exist infinitely many primes that divide P(n) for at least one positive integer n.
23.10.2022 19:24
I shall correct it according to your translation, everytime I use google translate and i think it might not make sense, I add the original wording thanks @ above
23.10.2022 19:30
@ above no problem
30.08.2023 03:23
In my opinion, the polynomial P should be "mit ganzzahligen Koeffizienten", i.e. "with integer coefficients"...
30.08.2023 05:02
is this not just the statement of schur
01.11.2024 20:30
Let $P \in \mathbb{Z}[x]$, $deg(P) = k \geq 1$ Assume there exist finitely many such primes $p_1, p_2, \cdots p_r$. Define $\mathbb{P} := \prod_{i=1}^r p_i$. Let $a_m$ denote the coefficient of lowest degree in $P$ such that $a_m \neq 0$. Now consider: \[ P(a_m\mathbb{P}^x) = \sum_{i=m}^k a_i \cdot (a_m\mathbb{P}^x)^i = (a_m)^{m+1}\mathbb{P}^{xm} \cdot \left( 1 + \sum_{i=m+1}^k a_i a_m^{i-m-1}\mathbb{P}^{x(i-m)} \right)\]The right term is arbitrarily large as we choose $x$ arbitrarily large and also coprime to $\mathbb{P}$ thus it must have some other new prime factor.