Let $x_1, \dots, x_N \in (0, \infty)$ each be a D993: Real number such that

(i)	$a \in (0, \infty)$ is a D3306: Real harmonic mean of $x_1, \dots, x_N$

Then \begin{equation} a = N \left( \sum_{n = 1}^N \frac{1}{x_n} \right)^{-1} \end{equation}