Find all composite numbers such that the positive divisors of greater than can be arranged on a circle so that no two adjacent ones are relatively prime.
Solution
When , arranging them as obviously satisfies the condition.
When , first arrange in order on the circle, then arrange the multiples of between and . The resulting arrangement satisfies the condition.
Finally, when , first place and on the circle, put the multiples of on one arc, and the multiples of on the other arc.
The remaining case cannot be achieved.
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