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 A119127 #12 Mar 31 2023 15:53:29
%S A119127 1,18,38,58,15306,28893,3851686,595216169886,53248694146381,
%T A119127 536869582203620058,14927275335718688666
%N A119127 Numbers k such that the k-th triangular number contains only digits {1,4,7}.
%H A119127 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr147.html">Tridigital Triangular Numbers</a>.
%Y A119127 Cf. A000217, A079654. See A119034 for a table of cross-references.
%K A119127 nonn,base,more
%O A119127 1,2
%A A119127 _Giovanni Resta_, May 10 2006
%E A119127 a(10)-a(11) from _Tyler Busby_, Mar 31 2023