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 A119227 #7 Jul 13 2021 21:31:58
%S A119227 10,34,109,3944509,4421714,10730871349,12472189525,3893060383753634
%N A119227 Numbers k such that the k-th triangular number contains only digits {5,7,9}.
%C A119227 Next term exceeds 1.4*10^16.
%H A119227 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr579.html">Tridigital Triangular Numbers</a>
%Y A119227 Cf. A000217, A119226. See A119034 for a table of cross-references.
%K A119227 nonn,base,more
%O A119227 1,1
%A A119227 _Giovanni Resta_, May 10 2006