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For $0\leq k\leq n$ write \[\binom{n}{k} = uv\] where the only primes dividing $u$ are in $[2,k]$ and the only primes dividing $v$ are in $(k,n]$.

Let $f(n)$ be the smallest $k$ such that $u>n^2$. Give bounds for $f(n)$.

A classical theorem of Mahler states that for any $\epsilon>0$ and integers $k$ and $l$ then, writing \[(n+1)\cdots (n+k) = ab\] where the only primes dividing $a$ are $\leq l$ and the only primes dividing $b$ are $>l$, we have $a < n^{1+\epsilon}$ for all sufficiently large (depending on $\epsilon,k,l$) $n$.

Mahler's theorem implies $f(n)\to \infty$ as $n\to \infty$, but is ineffective, and so gives no bounds on the growth of $f(n)$.

One can similarly ask for estimates on the smallest integer $f(n,k)$ such that if $m$ is the factor of $\binom{n}{k}$ containing all primes $\leq f(n,k)$ then $m > n^2$.