A229649 - OEIS

%I #14 Oct 22 2015 14:48:55

%S 1,4,28,232,2092,19864,195352,1970896,20275692,211825564,2240852928,

%T 23952708696,258285519688,2806105225928,30685515254240,

%U 337472968923532,3730218568024236,41417273400310152,461722437389957236,5166105817092273412

%N Cogrowth function of the group Baumslag-Solitar(7,7).

%C a(n) is the number of words of length 2n in the letters a,a^{-1},t,t^{-1} that equal the identity of the group BS(7,7)=<a,t | ta^7=a^7t>.

%H Murray Elder, <a href="/A229649/b229649.txt">Table of n, a(n) for n = 0..50</a>

%H M. Elder, A. Rechnitzer, E. J. Janse van Rensburg, T. Wong, <a href="http://arxiv.org/abs/1309.4184">The cogrowth series for BS(N,N) is D-finite</a>

%H <a href="/index/Gre#groups">Index entries for sequences related to groups</a>

%e For n=1 there are 4 words of length 2 equal to the identity: aa^{-1}, a^{-1}a, tt^{-1}, t^{-1}t.

%Y The cogrowth sequences for BS(N,N) for N = 1..10 are A002894, A229644, A229645, A229646, A229647, A229648, A229649, A229650, A229651, A229652.

%K nonn,walk

%O 0,2

%A _Murray Elder_, Sep 27 2013