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2015 China South East MO Grade 11 P4

Source: 2015 China South East MO Grade 11 P4

January 16, 2018
number theory

Problem Statement

Given 88 pairwise distinct positive integers a1,a2,,a8a_1,a_2,…,a_8 such that the greatest common divisor of any three of them is equal to 11. Show that there exists positive integer n8n\geq 8 and nn pairwise distinct positive integers m1,m2,,mnm_1,m_2,…,m_n with the greatest common divisor of all nn numbers equal to 11 such that for any positive integers 1p<q<rn1\leq p<q<r\leq n, there exists positive integers 1i<j81\leq i<j\leq 8 that aiajmp+mq+mra_ia_j\mid m_p+m_q+m_r.