%I #3 Mar 30 2012 16:49:06
%S 4,6,8,9,12,16,18
%N Gamma_0(n) has genus 0 and does not contain any elliptic elements.
%D J. McKay and A. Sebbar, Fuchsian groups, automorphic functions and Schwarzians, Math. Ann., 318 (2000), 255-275.
%K nonn,fini,full
%O 1,1
%A _N. J. A. Sloane_, Jun 27 2001