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MathNet 2014 Question 25

Math Olympiad Vault · MathNet 2014

Question 25

We call a composite positive integer $n$ nice if it is possible to arrange its factors that are larger than $1$ on a circle such that two neighboring numbers are not coprime. How many of the elements of the set $\{1, 2, 3, \ldots, 100\}$ are nice?