(2,m,n)-groups with Euler characteristic equal to -2^as^b
  We study those $(2,m,n)$-groups which are almost simple and for which the absolute value of the Euler characteristic is a product of two prime powers. All such groups which are not isomorphic to $PSL_2(q)$ or $PGL_2(q)$ are completely classified. 
Nick Gill
math.GR math.CO