Features of a high school olympiad problem

Abstract: This paper is a supplement to a talk for mathematics teachers given at the 2016 LSU Mathematics Contest for High School Students. The paper covers more details and aspects than could be covered in the talk. We start with an interesting problem from the 2009 Iberoamerican Math Olympiad concerning a particular sequence. We include a solution to the problem, but also relate it to several areas of mathematics. This problem demonstrates the countability of the rational numbers with a direct one-to-one correspondence. The problem also shows the one-to-one correspondence of finite continued fractions and rational numbers. The subsequence of odd indexed terms was constructed by Johannes Kepler and is discussed. We also show that the indices have an extension to the 2-adic integers giving a one-to-one correspondence between the positive real numbers and the 2-adic integers. Everything but the extension to the 2-adic integers is known to have appeared elsewhere.