Graph of eigenvalues of Maass forms of levels 100 to 1000 with $0 \leq R\leq 1$
The horizontal axis is the spectral parameter $R$ with the Laplace eigenvalue satisying $\lambda=1/4+R²$. The vertical axis is the level $N$. Each point corresponds to a Maass form of weight 0 and trivial character on $\Gamma_0(N)$ with the color showing whether the symmetry is even or odd. Clicking on a dot takes you to the homepage of the Maass form. For $N>100$ there are only results for prime level.
Examples of some ranges with complete data: