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 A119188 #13 Apr 06 2023 21:42:02
%S A119188 3,55,5735537337753,53737577757753,335355753333373553355,
%T A119188 573535753575353335777335733757755,
%U A119188 7357333757773777355335733737733553753
%N A119188 Triangular numbers composed of digits {3,5,7}.
%C A119188 a(8) > 10^37. - _Tyler Busby_, Mar 24 2023
%H A119188 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr357.html">Tridigital Triangular Numbers</a>.
%F A119188 a(n) = A000217(A119189(n)). - _Tyler Busby_, Mar 24 2023
%Y A119188 Cf. A000217, A119189. See A119033 for a table of cross-references.
%K A119188 nonn,base,more
%O A119188 1,1
%A A119188 _Giovanni Resta_, May 10 2006
%E A119188 a(6)-a(7) from _Tyler Busby_, Mar 24 2023