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MathNet 2018-part-05 — 181 problems (EN–VI) Question 63

Math Olympiad Vault · MathNet 2018-part-05 — 181 problems (EN–VI)

Question 63

Consider the infinite, strictly increasing sequence of positive integers $a_{n}$ such that

i. All terms of the sequence are pairwise coprime.

ii. The sum $\frac{1}{\sqrt{a_{1} a_{2}}} + \frac{1}{\sqrt{a_{2} a_{3}}} + \frac{1}{\sqrt{a_{3} a_{4}}} + \cdots$ is unbounded.

Prove that this sequence contains infinitely many primes.