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USAMO 2005 — Days 1 and 2 Question 1

USAMO · USAMO 2005 — Days 1 and 2

Question 1

Determine all composite positive integers $n$ for which it is possible to arrange all divisors of $n$ that are greater than $1$ in a circle so that no two adjacent divisors are relatively prime.

Proposed by Zuming Feng (credited in the supplied source).