Normal subgroups of low index in the modular group and other Hecke groups

Marston Conder and Peter Dobcsanyi

Abstract

An account is given of the determination of all normal subgroups of index up to $1500$ in the modular group PSL$(2,Z) cong C_2 * C_3$, and all normal subgroups of index up to $500$ in the Hecke groups $H_q = C_2 * C_q$ for $4 le q le 12$, using an adaptation of the low index subgroups algorithm.

Keywords
modular group, Hecke group, algorithm

Math Review Classification
Primary 20F05

Last Updated
6 June 2003

Length
23 pages

Availability
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