Abstract
In this paper, first, we determine the quotient groups of the Hecke groups H(λ q ), where q ≥ 7 is prime, by their principal congruence subgroups H p (λ q ) oflevel p, where p is also prime. We deal with the case of q = 7 separately, because of its close relation with the Hurwitz groups. Then, using the obtained results, we find the principal congruence subgroups of the extended Hecke groups \( \overline H \)(λ q ) for q ≥ 5 prime. Finally, we show that some of the quotient groups of the Hecke group H(λ q ) and the extended Hecke group \( \overline H \) (λ q ), q ≥ 5 prime, by their principal congruence subgroups H p (λ q ) are M*-groups.
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Ikikardes, S., Sahin, R. & Naci Cangul, I. Principal congruence subgroups of the Hecke groups and related results. Bull Braz Math Soc, New Series 40, 479–494 (2009). https://doi.org/10.1007/s00574-009-0023-y
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DOI: https://doi.org/10.1007/s00574-009-0023-y