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 A119205 #11 Mar 31 2023 03:20:41
%S A119205 9,10,3390,38589,12453549,3080826336474,298253071929010,
%T A119205 33089502135135685
%N A119205 Numbers k such that the k-th triangular number contains only digits {4,5,7}.
%H A119205 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr457.html">Tridigital Triangular Numbers</a>.
%Y A119205 Cf. A000217, A119204. See A119034 for a table of cross-references.
%K A119205 nonn,base,more
%O A119205 1,1
%A A119205 _Giovanni Resta_, May 10 2006
%E A119205 a(8) from _Tyler Busby_, Mar 31 2023