MathDB
Sequence

Source: Junior Olympiad of Malaysia Shortlist 2015 A4

July 17, 2015
algebranumber theory

Problem Statement

Suppose 2015=a1<a2<a3<<ak 2015= a_1 <a_2 < a_3<\cdots <a_k be a finite sequence of positive integers, and for all m,nN m, n \in \mathbb{N} and 1m,nk1\le m,n \le k , am+anam+n+mn a_m+a_n\ge a_{m+n}+|m-n| Determine the largest possible value k k can obtain.