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 A080038 #5 Jan 01 2024 18:13:53
%S A080038 3,3,4,3,3,4,3,3,4,4,3,3,4,3,3,4,3,3,4,4,3,3,4,3,3,4,3,3,4,4,3,3,4,4,
%T A080038 3,3,4,3,3,4,3,3,4,4,3,3,4,3,3,4,3,3,4,4,3,3,4,3,3,4,3,3,4,4,3,3,4,4,
%U A080038 3,3,4,3,3,4,3,3,4,4,3,3,4,3,3,4,3,3,4,4,3,3,4,3,3,4,3,3,4,4,3,3,4,4,3,3,4
%N A080038 Start with a(1)=3; apply 3 -> 343, 4 -> 3443; iterate.
%C A080038 a(n)= A080753(n+1) - A080753(n). Sum of first n terms + 2 = A080753(n).
%e A080038 3 -> 343 -> 3433443343 -> ...
%t A080038 SubstitutionSystem[{3->{3,4,3},4->{3,4,4,3}},{3},{5}][[1]] (* _Harvey P. Dale_, Jan 01 2024 *)
%Y A080038 Cf. A079000, A079948.
%K A080038 easy,nonn
%O A080038 1,1
%A A080038 _Matthew Vandermast_, Mar 14 2003