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 A053899 #14 Aug 11 2024 14:41:32
%S A053899 1,4,144,441,1444,7744,7447441,4147177477444,7174474747441,
%T A053899 1447471174444717444,117747174771111771147177144441,
%U A053899 7174471471414771441747147717441,1147111747441771474111741117114417444,4741471777144414774147714111744447747417744
%N A053899 Squares composed of digits {1,4,7}.
%H A053899 Author?, <a href="http://web.archive.org/web/20080708203024/http://blue.kakiko.com/mmrmmr/htm/eqtn06.html">Source</a>(<a href="http://web.archive.org/web/20060426155831/http://blue.kakiko.com/mmrmmr/txt/eqtn06.txt">txt</a>)
%H A053899 P. De Geest, <a href="https://www.worldofnumbers.com/threedigits.htm">Squares containing at most three distinct digits, Index entries for related sequences</a>
%H A053899 H. Mishima, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/math02/math0210.htm#147">Sporadic tridigital solutions</a>
%F A053899 a(n) = A053898(n)^2.
%Y A053899 Cf. A053898.
%K A053899 nonn,base
%O A053899 1,2
%A A053899 _Patrick De Geest_, Mar 15 2000
%E A053899 More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Jan 04 2005
%E A053899 Four more terms from Mishima's webpage added by _Max Alekseyev_, Jan 28 2012