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 A180727 #7 Mar 24 2020 15:04:08
%S A180727 1,21,37822859361,441,5842587018385982521381124421,
%T A180727 68122318582951682301,794280046581,85766121,9261,
%U A180727 10523016528610349434285830688358359761,1136272165922724266740722458520501,122694327386105632949003612841
%N A180727 Smallest power of 21 that begins with n.
%t A180727 With[{s=21^Range[0,100]},Table[SelectFirst[s,Take[IntegerDigits[ #], IntegerLength[ n]] == IntegerDigits[ n]&],{n,30}]]//Quiet (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Mar 24 2020 *)
%Y A180727 Cf. A180725, A180728, A180729
%K A180727 base,nonn
%O A180727 1,2
%A A180727 Daniel Mondot (dmondot(AT)gmail.com), Sep 18 2010