%I #8 Feb 26 2018 22:29:32
%S 2,12,242,2772,29282,320892,3543122,38987652,428717762,4715748972,
%T 51874849202,570624951732,6276856753442,69045406572252,
%U 759499667166482,8354496533703012,91899459727144322,1010894054854998732,11119834626984462962
%N Co-growth function of a certain group.
%D Stephen P Humphries, "Cogrowth of groups and the Dedekind-Frobenius group determinant", Mathematical Proceeding Cambridge Philosophical Society, volume 121 Part 2, pages 193-217 (1997).
%F a(n) = 2 * 11^(n-1) + (-1)^(n/2) * 5 * 11^(n/2-1) * (cos(Pi*n) + 1) [from Humphries]. _Sean A. Irvine_, Feb 26 2018
%K nonn
%O 1,1
%A _Stephen P. Humphries_
%E More terms from _Sean A. Irvine_, Feb 26 2018