Problem

Source: USAJMO 2024/3

Tags: AMC, USA(J)MO, USAJMO, Hi



Let $a(n)$ be the sequence defined by $a(1)=2$ and $a(n+1)=(a(n))^{n+1}-1$ for each integer $n\geq 1$. Suppose that $p>2$ is a prime and $k$ is a positive integer. Prove that some term of the sequence $a(n)$ is divisible by $p^k$. Proposed by John Berman