  We derive a fully explicit version of the Selberg trace formula for
twist-minimal Maass forms of weight 0 and arbitrary conductor and nebentypus
character, and apply it to prove two theorems. First, conditional on Artin's
conjecture, we classify the even 2-dimensional Artin representations of small
conductor; in particular, we show that the even icosahedral representation of
smallest conductor is the one found by Doud and Moore, of conductor 1951.
Second, we verify the Selberg eigenvalue conjecture for groups of small level,
improving on a result of Huxley from 1985.
