MathDB
Interesting number theory inXMO

Source: 16thXMO

June 22, 2024
arithmetic sequencenumber theorygreatest common divisor

Problem Statement

mm is an integer satisfying m2024m \ge 2024 , pp is the smallest prime factor of mm , for an arithmetic sequence {an}\{a_n\} of positive numbers with the common difference mm satisfying : for any integer 1ip21 \le i \le \frac{p}{2} , there doesn’t exist an integer x,ymax{a1,m}x , y \le \max \{a_1 , m\} such that ai=xya_i=xy Try to proof that there exists a positive real number cc such that for any 1ijn 1\le i \le j \le n , gcd(ai,aj)=c×gcd(i,j)gcd(a_i , a_j ) = c \times gcd(i , j)