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 A053973 #15 Aug 11 2024 14:41:32
%S A053973 9,676,69696,97969,9696996,9697699776769,77797697969777769,
%T A053973 776797677679677696,6776696769676669969,9767769967769766976,
%U A053973 97667999767779769677969,7676999976999997667777796,69997676676669667699797969,67976976676979976697777676769,96667776776767999797799699976676
%N A053973 Squares composed of digits {6,7,9}.
%H A053973 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 A053973 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 A053973 Hisanori Mishima, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/math02/math0210.htm#679">Sporadic tridigital solutions</a>
%F A053973 a(n) = A053972(n)^2.
%t A053973 Flatten[Table[Select[FromDigits/@Tuples[{6,7,9},i],IntegerQ[Sqrt[#]]&],{i,23}]] (* _Harvey P. Dale_, Dec 07 2014 *)
%Y A053973 Cf. A053972.
%K A053973 nonn,base
%O A053973 1,1
%A A053973 _Patrick De Geest_, Mar 15 2000
%E A053973 More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Jan 14 2005
%E A053973 a(12)-a(15) from Mishima's website, added by _Max Alekseyev_, Nov 30 2017