@article{01656123,
title = {Power subgroups of Hecke groups },
journal = {International Journal of Mathematics and Mathematical Sciences},
volume = {25},
year = {2001},
pages = {703-708},
doi = {10.1155/S0161171201005993},
zbl = {1012.11032},
language = {en},
url = {http://dml.mathdoc.fr/item/01656123}
}
Yilmaz, Nihal; Cangül, I.Naci. Power subgroups of Hecke groups . International Journal of Mathematics and Mathematical Sciences, Tome 25 (2001) pp. 703-708. doi : 10.1155/S0161171201005993. http://gdmltest.u-ga.fr/item/01656123/