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MathNet 2026 — Part 03 Question 59

Math Olympiad Vault · MathNet 2026 — Part 03

Question 59

We say that a positive integer $n$ is fantastic, if there exist positive rational numbers $a$ and $b$ such that

$$
n = a + \frac{1}{a} + b + \frac{1}{b}.
$$


a. Prove that there exist infinitely many prime numbers $p$ such that no multiple of $p$ is fantastic.

b. Prove that there exist infinitely many prime numbers $p$ such that some multiple of $p$ is fantastic.