The Schur multiplier and the outer automorphism group are both trivial.
Conway and Norton suggested in their 1979 paper that monstrous moonshine is not limited to the monster, but that similar phenomena may be found for other groups.
Larissa Queen and others subsequently found that one can construct the expansions of many Hauptmoduln from simple combinations of dimensions of sporadic groups.
where one can set the constant term a(0) = 42 (OEIS: A030197), and η(τ) is the Dedekind eta function.
Kleidman, Parker & Wilson (1989) found the 14 conjugacy classes of maximal subgroups of Fi23 as follows: