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Erdős problem 390

Let f(n)f(n) be the least mm for which n!n! can be written as a1aka_1\cdots a_k with n<a1<<ak=mn < a_1 < \cdots < a_k = m - the smallest possible largest factor in a factorization of n!n! into distinct integers all exceeding nn. Erdős, Guy and Selfridge proved f(n)2nn/lognf(n) - 2n \asymp n/\log n. Erdős asked whether there is a constant cc with f(n)2ncnlogn,f(n) - 2n \sim c\,\frac{n}{\log n}, and what it is.

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Let $f(n)$ be the least $m$ for which $n!$ can be written as $a_1\cdots a_k$ with $n < a_1 < \cdots < a_k = m$ - the smallest possible largest factor in a factorization of $n!$ into distinct integers all exceeding $n$. Erdős, Guy and Selfridge proved $f(n) - 2n \asymp n/\log n$. Erdős asked whether there is a constant $c$ with $$f(n) - 2n \sim c\,\frac{n}{\log n},$$ and what it is. This preprint answers yes and names the constant: $$\lim_{n\to\infty}\frac{(f(n)-2n)\log n}{n} = \frac{4029639598}{25970038185} \approx 0.15516.$$

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