IMO 2020 Shortlist N7
Let S be a set consisting of n ě 3 positive integers, none of which is a sum of two other distinct members of S. Prove t...
Category: Number Theory
Problem
Let S be a set consisting of n ě 3 positive integers, none of which is a sum of two
other distinct members of S. Prove that the elements of S may be ordered as a1,a2,...,an so
that ai does not divide ai´1 ai1 for all i “ 2,3,...,n ´ 1.
(Ukraine) Shortlisted problems 11 12 Saint-Petersburg — Russia, 18th–28th September 2020