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 A119173 #10 Jul 13 2021 07:23:20
%S A119173 3,11,23,36,123,3651,394123,2307651,74534188,394392348,3639430251,
%T A119173 1159885996348
%N A119173 Numbers k such that the k-th triangular number contains only digits {2,6,7}.
%C A119173 Next term exceeds 4.4*10^18.
%H A119173 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr267.html">Tridigital Triangular Numbers</a>
%Y A119173 Cf. A000217, A119172. See A119034 for a table of cross-references.
%K A119173 nonn,base,more
%O A119173 1,1
%A A119173 _Giovanni Resta_, May 10 2006
%E A119173 Lower bound for further terms updated by _Max Alekseyev_, May 07 2009