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 A119221 #11 Mar 31 2023 03:20:04
%S A119221 3,10,11,36,105,108,114,1316,3363,105516,343091,1316705,3657011,
%T A119221 10638485,13310789,33336636,37028788,1145936870,108320504576528,
%U A119221 3333333366663363,105725008289010683
%N A119221 Numbers k such that the k-th triangular number contains only digits {5,6,8}.
%H A119221 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr568.html">Tridigital Triangular Numbers</a>.
%Y A119221 Cf. A000217, A119220. See A119034 for a table of cross-references.
%K A119221 nonn,base,more
%O A119221 1,1
%A A119221 _Giovanni Resta_, May 10 2006
%E A119221 a(21) from _Tyler Busby_, Mar 31 2023