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 A307255 #20 Apr 10 2019 22:28:38
%S A307255 0,1,2,3,133302001,132303132012,131312312013231,132000312313232,
%T A307255 123111200333000032,130330012131021302,131011302011130113,
%U A307255 122132323102303012312,130030202001033022111,113333330333220330011201,121222313212022110233320,113121021032311213311133001,120320123012330002303131013
%N A307255 Numbers k such that k is the substring identical to the most significant digits of its base-4 representation.
%C A307255 Numbers k whose base-4 representation begins with the same digits as k itself.
%H A307255 Scott R. Shannon, <a href="/A307255/b307255.txt">Table of n, a(n) for n = 1..500</a>
%e A307255 133302001_10 = 13330200123301_4, which also begins with '133302001'.
%t A307255 With[{b = 4}, Select[Array[{FromDigits@ #, #} &@ IntegerDigits[#, b] &, b^12, 0], Take[IntegerDigits[First@ #, b], Length@ Last@ #] == Last[#] &][[All, 1]]] (* _Michael De Vlieger_, Apr 01 2019 *)
%Y A307255 This is a subsequence of A038104.
%K A307255 nonn,base
%O A307255 1,3
%A A307255 _Scott R. Shannon_, Apr 01 2019