A018231 - OEIS

%I #9 Feb 05 2019 21:06:05

%S 1,2,3,4,8,9,12,16,18,27,32,36,48,64,72,108,128,144,192,256,288,432,

%T 576,1152,1728,2304

%N Numbers n such that normalizer of Gamma_0(n) is a triangle group.

%D M. Akbas and D. Singerman, The signature of the normalizer Gamma_0(N), in Graphs, Combinatorics and Geometry, ed. Liebeck and Saxl, LMSLNS 165, Cambridge Univ. Press, 1992, 77-86.

%Y Cf. A018229, A018228, A018230.

%K nonn,fini,full

%O 1,2

%A _N. J. A. Sloane_.

%E Missing terms 256 and 2304 added, list sorted, and keywords added by _Sean A. Irvine_, Feb 05 2019