A note on some modular subgroups. (Q2566510)

Here the author introduces some modular subgroups and calculates parabolic class numbers, which is the number of non-isomorphic conjugacy classes of parabolic elements, of those groups. He gives a formula for the parabolic class number of some special subgroups, in terms of the formula given before for the congruence subgroups of the modular group of level \(n\). This work is the continuation, and in some sense, a special case of the author's work on Hecke groups which are just a kind of generalisation of the well known modular group.