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Problem #372: Let $P(n)$ denote the largest prime factor of $n$

Let $P(n)$ denote the largest prime factor of $n$. There are infinitely many $n$ such that $P(n)>P(n+1)>P(n+2)$.

Problem Statement

Let $P(n)$ denote the largest prime factor of $n$. There are infinitely many $n$ such that $P(n)>P(n+1)>P(n+2)$.

Categories: Number Theory

Progress

Conjectured by Erdős and Pomerance [ErPo78], who proved the analogous result for $P(n)<P(n+1)<P(n+2)$. Solved by Balog [Ba01], who proved that this is true for $\gg \sqrt{x}$ many $n\leq x$ (for all large $x$). Balog suggests the natural conjecture that the density of such $n$ is $1/6$. A generalised form of this conjecture was presented by De Koninck and Doyon [DeDo11].

Source: erdosproblems.com/372 | Last verified: January 14, 2026

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