MathDB
Collinarity

Source: RMO 2019 P6

October 24, 2019

Problem Statement

Suppose 9191 distinct positive integers greater than 11 are given such that there are at least 456456 pairs among them which are relatively prime. Show that one can find four integers a,b,c,da, b, c, d among them such that gcd⁡(a,b)=gcd⁡(b,c)=gcd⁡(c,d)=gcd⁡(d,a)=1.\gcd(a,b)=\gcd(b,c)=\gcd(c,d)=\gcd(d,a)=1.
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