number-theory / Number theory

Erdős Problem #387

Erdős and Graham asked whether $\binom{n}{k}$ with $1 \le k \le n/2$ must always have a divisor $\le n$ that is close to $n$, meaning bigger than a fixed constant times $n$. Settled in both directions: true when $k$ is large enough as a function of $n$, but false in general, since there are $\binom{n}{k}$ with $k$ small compared to $n$ having no such divisor.

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number-theoryMay 20, 2026Significance 35/100Registry: unreviewed

Erdős Problem #387

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false in general; the positive direction holds for k large relative to n

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Erdős and Graham asked whether $\binom{n}{k}$ with $1 \le k \le n/2$ must always have a divisor $\le n$ that is close to $n$, meaning bigger than a fixed constant times $n$. Settled in both directions: true when $k$ is large enough as a function of $n$, but false in general, since there are $\binom{n}{k}$ with $k$ small compared to $n$ having no such divisor.

false in general; the positive direction holds for k large relative to n

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