@article{GDZPPN002112523,
title = {Subgroup growth and congruence subgroups.},
journal = {Inventiones mathematicae},
volume = {121},
year = {1995},
pages = {267-296},
zbl = {0848.20036},
url = {http://dml.mathdoc.fr/item/GDZPPN002112523}
}
Lubotzky, Alexander. Subgroup growth and congruence subgroups.. Inventiones mathematicae, Tome 121 (1995) pp. 267-296. http://gdmltest.u-ga.fr/item/GDZPPN002112523/