%I
%S 1,12,1296,505536,679848192,3248147205120,57637071142391808,
%T 3930578658351563587584,1050888530707010579202637824,
%U 1112792971262327168651248131637248
%N Number of elements of length n with respect to the natural metric in the special group of rational series over the finite field F_2 in two noncommuting variables.
%H Roland Bacher, Apr 08 2008, <a href="/A137343/b137343.txt">Table of n, a(n) for n = 0..14</a>
%H R. Bacher, <a href="http://arxiv.org/abs/0804.1092">The special subgroup of invertible noncommutative rational power series as a metric group</a>, arXiv:0804.1092
%F The reference contains a somewhat complicated formula.
%K nonn
%O 0,2
%A _Roland Bacher_, Apr 08 2008
