number-theory / Number Theory, Binomial Coefficients

Erdős Problem #684

For the least $k$ at which the small-prime part of $\binom{n}{k}$ exceeds $n^2$, how large can $f(n)$ be?

10Significance / 100
1Frontier events
0Verification tasks
0Recorded attempts

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number-theoryJul 25, 2026Significance 10/100Registry: contested

Erdős Problem #684

Prior state unknownproved

For the least $k$ at which the small-prime part of $\binom{n}{k}$ exceeds $n^2$, how large can $f(n)$ be?

SourceReplayReproducedFormal proofStatement auditExternal checkExpert reviewPeer review! Disputed

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Invalidated

For the least $k$ at which the small-prime part of $\binom{n}{k}$ exceeds $n^2$, how large can $f(n)$ be?

A preprint claimed $\limsup f(n)/\log n = \infty$, but a deterministic audit later found a counterexample to its key Lemma 18. The stated conclusion is not established and the problem remains open.

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