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 A180728 #12 May 14 2023 17:22:16
%S A180728 0,1,8,2,21,15,9,6,3,28,25,22,19,16,13,10,38,7,4,32,1,29,26,85,23,82,
%T A180728 20,79,48,17,45,14,73,42,11,39,8,67,36,5,64,33,362,2,61,30,89,58,387,
%U A180728 27,86,55,384,24,83,52,1191,21,80,1219,49,288,18,77,946,46,285,15,74,1483,43
%N A180728 21^a(n) is smallest power of 21 beginning with n.
%H A180728 D. Mondot, <a href="/A180728/b180728.txt">Table of n, a(n) for n=1..32699</a>
%t A180728 Module[{nn=1500,t21},t21=Table[{n,IntegerDigits[21^n]},{n,0,nn}];Table[SelectFirst[ t21,IntegerDigits[k]==Take[#[[2]],IntegerLength[k]]&],{k,80}]][[;;,1]]//Quiet (* _Harvey P. Dale_, May 14 2023 *)
%Y A180728 Cf. A180726, A180727, A180730
%K A180728 base,nonn
%O A180728 1,3
%A A180728 _Daniel Mondot_, Sep 18 2010