@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/