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Reference: erdosproblems.com/376
Are there infinitely many $n$ such that ${2n\choose n}$ is coprime to $105$?
Erdős, Graham, Ruzsa, and Straus [EGRS75] have shown that, for any two odd primes $p$ and $q$, there are infinite many $n$ such that ${2n\choose n}$ is coprime to $pq$.