On the normalizer of the congruence subgroup $H^5_0 (I)$ of the Hecke group $H^5$

Abstract

Let $lambda = 2cos frac{pi}{5}$ and let $H^5$ be the Hecke group associated to $lambda$. In this paper, the normalizersof the congruence subgroups $H^5_0 (I)$ in $PSL(2,Bbb{Z}[lambda])$ are studied in the case where $I = (2)^{alpha}I', (2, I')$ = 1 and I' is a prime ideal.