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MathNet 2017-part-05 — 176 problems (EN–VI) Question 109

Math Olympiad Vault · MathNet 2017-part-05 — 176 problems (EN–VI)

Question 109

Assume that $n$ is a composite positive integer. For each its proper divisor $d$, we write down the number $d+1$ on the board. Find all values of $n$ for which the written numbers appear to be exactly all the proper divisors of some positive integer $m$. (A proper divisor of a positive integer $a \gt 1$ is any its positive divisor distinct from 1 and $a$.)