OPEN
This is open, and cannot be resolved with a finite computation.
Let $g(k)>k+1$ be the smallest $n$ such that all prime factors of $\binom{n}{k}$ are $>k$. Estimate $g(k)$.
A question of Ecklund, Erdős, and Selfridge
[EES74], who proved\[k^{1+c}<g(k)\leq \exp((1+o(1))k)\]for some constant $c>0$, and conjectured $g(k)<L_k=[1,\ldots,k]$, the least common multiple of all integers $\leq k$, for all large $k$. In
[EES74] they further conjecture that\[\limsup \frac{g(k+1)}{g(k)}=\infty\]and\[\liminf \frac{g(k+1)}{g(k)}=0.\]The lower bound was improved by Erdős, Lacampagne, and Selfridge
[ELS93] and Granville and Ramaré
[GrRa96]. The current record is\[g(k) \gg \exp(c(\log k)^2)\]for some $c>0$, due to Konyagin
[Ko99b].
Erdős, Lacampagne, and Selfridge
[ELS93] write 'it is clear to every right-thinking person' that $g(k)\geq\exp(c\frac{k}{\log k})$ for some constant $c>0$.
Sorenson, Sorenson, and Webster
[SSW20] give heuristic evidence that\[\log g(k) \asymp \frac{k}{\log k}.\]See also
[1094].
View the LaTeX source
This page was last edited 12 January 2026.
Additional thanks to: Amelburg and Jake Mallen
When referring to this problem, please use the original sources of Erdős. If you wish to acknowledge this website, the recommended citation format is:
T. F. Bloom, Erdős Problem #1095, https://www.erdosproblems.com/1095, accessed 2026-01-16