MathDB
Sequence

Source: Junior Olympiad of Malaysia Shortlist 2015 A8

July 17, 2015
algebra

Problem Statement

Let a1,a2,,a2015 a_1,a_2, \cdots ,a_{2015} be 20152015-tuples of positive integers (not necessary distinct) and let k k be a positive integers. Denote f(i)=ai+a1a2a2015ai\displaystyle f(i)=a_i+\frac{a_1a_2 \cdots a_{2015}}{a_i} .
a) Prove that if k=20152015 k=2015^{2015} , there exist a1,a2,,a2015 a_1, a_2, \cdots , a_{2015} such that f(i)=k f(i)= k for all 1i20151\le i\le 2015 .\\ b) Find the maximum k0k_0 so that for kk0k\le k_0, there are no kk such that there are at least 2 2 different 20152015-tuples which fulfill the above condition.