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 A119220 #17 Mar 27 2023 01:26:15
%S A119220 6,55,66,666,5565,5886,6555,866586,5656566,5566865886,58855888686,
%T A119220 866856686865,6686866555566,56588686866855,88588558556655,
%U A119220 555665666566566,685565588888866,656585655585666885,5866665855856865856556555656,5555555666655656666556566566566,5588888688855688866886555588568586
%N A119220 Triangular numbers composed of digits {5,6,8}.
%C A119220 All terms except the first end in 55, 56, 65, 66, 85 or 86. - _Robert Israel_, Mar 26 2023
%H A119220 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr568.html">Tridigital Triangular Numbers</a>.
%F A119220 a(n) = A000217(A119221(n)). - _Tyler Busby_, Mar 26 2023
%Y A119220 Cf. A000217, A119221. See A119033 for a table of cross-references.
%K A119220 nonn,base
%O A119220 1,1
%A A119220 _Giovanni Resta_, May 10 2006
%E A119220 a(19)-a(21) from _Tyler Busby_, Mar 26 2023