|
%I #31 Oct 22 2015 14:48:23
%S 1,4,28,244,2396,25324,281140,3232352,38151196,459594316,5628197948,
%T 69859456440,876985904276,11115789165888,142066687799680,
%U 1828884017527504,23694360858872604,308714491495346028,4042605442981407388,53178663502737007352
%N Cogrowth function of the group Baumslag-Solitar(2,2).
%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(2,2)=<a,t | ta^2=a^2t>.
%H Murray Elder, <a href="/A229644/b229644.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 Wikipedia, <a href="http://en.wikipedia.org/wiki/Baumslag%E2%80%93Solitar_group">Baumslag-Solitar group</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
|
