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A lot of squares. Can all of them be different?

Source: Serbia Math Olympiad 2016 P6

April 2, 2016
number theorynumber theory unsolved

Problem Statement

Let a1,a2,,a22016a_1, a_2, \dots, a_{2^{2016}} be positive integers not bigger than 20162016. We know that for each n22016n \leq 2^{2016}, a1a2an+1a_1a_2 \dots a_{n} +1 is a perfect square. Prove that for some ii , ai=1a_i=1.