  Let G be a finitely generated group and M_n(G) the number of its normal
subgroup subgroups of index at most n. For linear groups G we show that M_n(G)
can grow polynomially in n only if the semisimple part of the Zariski closure
of G has simple components only of type G2, F4 or E8 (and in this case indeed
this can happened!)
