Problem #308: Let $N\geq 1$. What is the smallest integer not...

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Progress

This was essentially solved by Croot [Cr99], who proved that if $f(N)$ is the smallest integer not representable then\[\left\lfloor\sum_{n\leq N}\frac{1}{n}-\frac{9}{2}(1+o(1))\frac{(\log\log N)^2}{\log N}\right\rfloor\leq f(N)\]and\[f(N)\leq \left\lfloor\sum_{n\leq N}\frac{1}{n}-\frac{1}{2}(1+o(1))\frac{(\log\log N)^2}{\log N}\right\rfloor.\]It follows that, if $m_N=\lfloor \sum_{n\leq N}\frac{1}{n}\rfloor$, then the set of integers representable is, for all $N$ sufficiently large, either $\{1,\ldots,m_N-1\}$ or $\{1,\ldots,m_N\}$.