@Article{LanguascoZaccagnini2010b, Author = "A. Languasco and A. Zaccagnini", Title = "Computing the {Mertens} and {Meissel}--{Mertens} constants for sums over arithmetic progressions", Journal = "Experiment. Math.", Volume = 19, Issue = 3, Pages = "279--284", Note = "\url{http://arxiv.org/abs/0906.2132}", Year = 2010, Abstract = "We give explicit numerical values with $100$ decimal digits for the Mertens constant involved in the asymptotic formula for $\sum_{\substack{p \le x \\ p \equiv a \bmod q}} 1 / p$ and, as a by-product, for the Meissel-Mertens constant defined as $\sum_{p \equiv a \bmod q} (\log(1-1/p)+1/p)$, for $q \in \{3$, \dots, $100\}$ and $(q, a) = 1$." }