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MathNet 2022-part-02 — 197 problems (EN–VI) Question 36

Math Olympiad Vault · MathNet 2022-part-02 — 197 problems (EN–VI)

Question 36

We call positive integers $n, m$ an *interesting pair* if $n \lt m$ and the greatest prime factor of $n$ is equal to the greatest prime factor of $m$.

a. For an interesting pair $n, m$, will there always exist a prime $p$ such that $n \lt p \lt m$?

b. Among the first 25 positive integers, how many don't form an interesting pair with any smaller positive integer?