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 A053881 #19 Sep 29 2024 00:07:19
%S A053881 1,4,121,144,441,1444,114244,2214144,11142244,121242121,421111441,
%T A053881 1111422244,44424414441,111114222244,11111142222244,214222214414224,
%U A053881 242441124211441,411244411422244,1111111422222244,2111211444222241
%N A053881 Squares composed of digits {1,2,4}.
%C A053881 Includes all numbers of the form ((10^k-1)/3 + 5)^2 for k > 1. - _Andrew Howroyd_, Sep 28 2024
%H A053881 Zhao Hui Du, <a href="/A053881/b053881.txt">Table of n, a(n) for n = 1..54</a>
%H A053881 Patrick De Geest, <a href="http://www.worldofnumbers.com/threedigits.htm">Squares containing at most three distinct digits, Index entries for related sequences</a>
%F A053881 a(n) = A053880(n)^2.
%e A053881 Terms include 1444, 114244, 11142244, 1111422244, 111114222244, 11111142222244, etc. - _Andrew Howroyd_, Sep 28 2024
%Y A053881 Cf. A053880.
%K A053881 nonn,base
%O A053881 1,2
%A A053881 _Patrick De Geest_, Mar 15 2000