\begin{definition}[Definition:Meissel-Mertens Constant]
Consider the expression:
:$\ds M = \map {\lim_{n \mathop \to \infty} } {\sum_{\substack {p \mathop \le n \\ \text {$p$ prime} } } \dfrac 1 p - \ln \ln p}$
Then:
:$M \approx 0 \cdotp 26149 \, 72128 \, 47642 \, 78375 \, 54268 \, 38608 \, 69585 \, 90516 \ldots$
{{OEIS|A077761}}
The constant $M$ is known as the '''Meissel-Mertens Constant'''.
\end{definition}