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 A038104 #13 May 17 2019 02:34:24
%S A038104 0,1,2,3,3320,3321,3322,3323,112000,112001,112002,112003,121322,
%T A038104 121330,211320,211321,211322,211323,320232,320302,321230,321301,
%U A038104 322222,323221,323320,323321,323322,323323,10030333,20332101,30132120,30132121
%N A038104 Numbers n with property that n is a substring of its base 4 representation.
%H A038104 Giovanni Resta, <a href="/A038104/b038104.txt">Table of n, a(n) for n = 1..107</a> (terms < 10^16)
%e A038104 323323 = base 10 -> 1032{323323} = base 4.
%Y A038104 Cf. A038102-A038106, A228050-A228052, A227549.
%K A038104 nonn,base
%O A038104 1,3
%A A038104 _Patrick De Geest_, Feb 15 1999