Original post is here: eklausmeier.goip.de
Just the problematic code without anything else surrounding it: $n/\log n$.
Looks good, so far. Now more text surrounding it: This time the logarithm is not formatted as expected.
Twin primes are two primes $p$ and $p+2$. The ancient twin prime conjecture asserts that there are infinitely many twin primes. (This conjecture is still not proved.) The prime number theorem asserts that there are (asymptotically) $n/log n$ primes whose value is smaller than a positive integer $n$, and this implies that we can find arbitrary large pairs of consecutive primes $p$ and $q$ such that $q-p$ is at most $(\log p)$.
This is in reply to latex-nlog-n-does-not-work.