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x, y relatively prime to 5 such that x^2 + y^2 = 5^n for any n

Source: KJMO 2008 p3

May 2, 2019
number theoryrelatively primeDiophantine equationcoprime

Problem Statement

For all positive integers nn, prove that there are integers x,yx, y relatively prime to 55 such that x2+y2=5nx^2 + y^2 = 5^n.