A Database of Modular Forms on Noncongruence Subgroups

Abstract

We present a database of several hundred modular forms up to and including weight six on noncongruence subgroups of index ≤ 17. In addition, our database contains expressions for the Belyi map for genus zero subgroups and equations of the corresponding elliptic curves for genus one subgroups and numerical approximations of noncongruence Eisenstein series to 1500 digits precision.