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 A119066 #8 Jul 13 2021 01:20:29
%S A119066 2,24,37,77,775,3943940,7844837,124153399,393193023940,78406253666877,
%T A119066 256907649052235,1240997802874797
%N A119066 Numbers k such that the k-th triangular number contains only digits {0,3,7}.
%C A119066 Next term exceeds 1.4*10^16.
%H A119066 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr037.html">Tridigital Triangular Numbers</a>
%Y A119066 Cf. A000217, A119065. See A119034 for a table of cross-references.
%K A119066 nonn,base,more
%O A119066 1,1
%A A119066 _Giovanni Resta_, May 10 2006