Problem

Source: Romania JBMO TST 2022 Day 2 Problem 2

Tags: number theory, Romanian TST, JBMO TST



Find the largest positive integer $n$ such that the following is true: There exists $n$ distinct positive integers $x_1,~x_2,\dots,x_n$ such that whatever the numbers $a_1,~a_2,\dots,a_n\in\left\{-1,0,1\right\}$ are, not all null, the number $n^3$ do not divide $\sum_{k=1}^n a_kx_k$.