IMC 2023 · Problem 10

Day 230th IMC · Blagoevgrad, Bulgaria

Statement

For every positive integer nn, let f(n),g(n)f(n), g(n) be the minimal positive integers such that

1+11!+12!++1n!=f(n)g(n).1 + \frac{1}{1!} + \frac{1}{2!} + \ldots + \frac{1}{n!} = \frac{f(n)}{g(n)}.

Determine whether there exists a positive integer nn for which g(n)>n0.999ng(n) > n^{0.999n}.

Official solution

Hidden so you can work on the problem first.

Proposed by Fedor Petrov, St. Petersburg State University.