(1) School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, E1 4NS London, United Kingdom;(2) Mathematisches Institut, Albert-Ludwigs-Universität, Eckerstr. 1, 79104 Freiburg, Germany
Abstract:
For a finitely generated group $\Gamma$, denote by
the number of normal subgroups of index
n. A. Lubotzky proved that for the free group
Fr of rank r,
is of type nlogn. We show that the same is
true for a much larger class of groups. On the other hand we show that
for almost all n, the inequality
<
holds true for every
r-generated group $\Gamma$.Received: 30 October 2002