Problem

Source: IMOC 2021 N10

Tags: number theory, IMOC



A prime is called perfect if there is a permutation $a_1, a_2, \cdots, a_{\frac{p-1}{2}}, b_1, b_2, \cdots, b_{\frac{p-1}{2}}$ of $1, 2, \cdots, p-1$ satisfies $$b_i \equiv a_i + \frac{1}{a_i} \pmod p$$for all $1 \le i \le \frac{p-1}{2}$. Show that there are infinitely many primes that are not perfect. Proposed By - CSJL