[1] Akbas M, Singerman D. The signature of the normalizer of London Math Soc Lecture Notes Series,
1992, 165: 77-86

[2] Conway J H, Norton S P. Monstrous moonshine. Bull London Math Soc, 1979, 11: 308-339

[3] Kern-Isberner G, Rosenberger G. A note on numbers of the form n = x2 + Ny2. Arch Math, 1984, 43:
148-156

[4] Jones G A, Singerman D. Complex Functions: An Algebraic and Geometric Viewpoint. Cambridge:
Cambridge University Press, 1987

[5] Keskin R. On the parabolic class number of some subgroups of Hecke groups. Turkish Journal of Mathe-
matics, 1998, 22(2): 199-205

[6] Keskin R. On the parabolic class numbers of some Fuchsian groups. Note di Matematica, 1999, 19(2):
275-283

[7] Maclachlan C. Groups of units of zero ternary quatratic forms. Proceedings of the Royal Society of
Edinburg, 1981, 88A: 141-157

[8] Miyake T. Modular Forms. Springer-Verlag, 1989

[9] Rose H E. A Course in Number Theory. Oxford Science Publications, 1994

[10] Schoeneberg B. Elliptic Modular Functions. Berlin, Heidelberg, New York: Springer-Verlag, 1974

[11] Singerman D. Subgroups of Fuchsian groups and finite permutation groups. Bulletin London Math Soc,
1970, 2: 319-323

[12] Shimura G. Introduction to the Arithmetic Theory of Automorphic Functions. Princeton Univ Press, 1971