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 A218402 #17 Jul 13 2021 07:24:17
%S A218402 44,426096444,12641976109035254775
%N A218402 Numbers k such that the k-th triangular number contains only digits {0,7,9}.
%C A218402 No other terms below 1.4*10^20.
%H A218402 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr079.html">Tridigital Triangular Numbers</a>
%Y A218402 Cf. A000217, A218401. See A119034 for a table of cross-references.
%K A218402 base,nonn,more,hard,bref
%O A218402 1,1
%A A218402 _Max Alekseyev_, Oct 28 2012