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%I #8 Apr 01 2015 17:10:39
%S 1,4,240,52032,37961472,95557604352,873176389545984,
%T 30234012628981334016,4073184753921806027390976,
%U 2164965110784257951109280432128,4571419424684923104187906920444592128
%N Number of rational series having complexity n over the finite field F_2 in two non-commuting variables.
%H Roland Bacher, Apr 08 2008, <a href="/A137342/b137342.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 non-commutative 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
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