Which harmonic numbers have prime numerators?
Solution 1:
As a partial answer, see Wolstenholme’s theorem: for a prime $p > 3$, the numerator of $H_{p-1}$ is divisible by $p^2$, where
$$ H_{p-1} \equiv \sum_{n=1}^{p-1} \frac{1}{n} $$
Which harmonic numbers have prime numerators?
Solution 1:
As a partial answer, see Wolstenholme’s theorem: for a prime $p > 3$, the numerator of $H_{p-1}$ is divisible by $p^2$, where
$$ H_{p-1} \equiv \sum_{n=1}^{p-1} \frac{1}{n} $$