This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A106826 #10 Oct 01 2016 21:16:29
%S A106826 2,3,4,3,4,1,4,3,4,1,2,1,4,1,4,3,4,1,2,1,2,3,2,1,4,1,2,1,4,1,4,3,4,1,
%T A106826 2,1,2,3,2,1,2,3,4,3,2,3,2,1,4,1,2,1,2,3,2,1,4,1,2,1,4,1,4,3,4,1,2,1,
%U A106826 2,3,2,1,2,3,4,3,2,3,2,1,2,3,4,3,4,1,4,3,2,3,4,3,2,3,2,1,4,1,2,1,2,3,2,1,2
%N A106826 Trajectory of 1 under the morphism 1->{2,1}, 2->{2,3}, 3->{4,3}, 4->{4,1}.
%C A106826 This is the reverse of the morphism in A105500 and the trajectory of 1 actually starts with 2 instead of 1.
%H A106826 F. M. Dekking, <a href="http://dx.doi.org/10.1016/0001-8708(82)90066-4">Recurrent sets</a>, Advances in Mathematics, vol. 44, no. 1 (1982), 78-104.
%H A106826 <a href="/index/Fi#FIXEDPOINTS">Index entries for sequences that are fixed points of mappings</a>
%t A106826 Nest[ Flatten[ # /. {1 -> {2, 1}, 2 -> {2, 3}, 3 -> {4, 3}, 4 -> {4, 1}}] &, {1}, 8] (*_Robert G. Wilson v_, Jun 20 2005 *)
%o A106826 (PARI) {a(n)=local(A);if(n<0, 0, n++; A=[2]; while(length(A)<n, A=concat(vector(length(A),k,[[2,1],[2,3],[4,3],[4,1]][A[k]]))); A[n])}
%Y A106826 Cf. A105500.
%K A106826 nonn,easy
%O A106826 0,1
%A A106826 _N. J. A. Sloane_, May 20 2005