%I #4 Mar 30 2012 17:34:15
%S 4,3,2,1,4,3,2,1,4,2,1,4,1,4,4,3,2,1,4,3,2,1,4,2,1,4,1,4,4,3,2,1,4,2,
%T 1,4,1,4,4,3,2,1,4,1,4,4,3,2,1,4,4,3,2,1,4,3,2,1,4,2,1,4,1,4,4,3,2,1,
%U 4,3,2,1,4,2,1,4,1,4,4,3,2,1,4,2,1,4,1,4,4,3,2,1,4,1,4,4,3,2,1,4,4,3,2,1,4
%N Four-symbol substitution, characteristic polynomial: x^4-x^3-1.
%C This substitution is associated with the Theta(1) Pisot number. Digraph matrix is: {{0, 1, 0, 0}, {0, 0, 1, 0}, {0, 0, 0, 1}, {1, 0, 0, 1}}
%F 1->{2}, 2->{3}, 3->{4}, 5->{1, 4}
%t s[1] = {2}; s[2] = {3}; s[3] = {4}; s[4] = {1, 2, 3}; t[a_] := Flatten[s /@ a]; p[0] = {1}; p[1] = t[p[0]]; p[n_] := t[p[n - 1]] aa = p[19]
%K nonn,uned
%O 0,1
%A _Roger L. Bagula_, May 12 2005