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 A119151 #8 Jul 13 2021 07:26:44
%S A119151 1,13,61,133,613,1333,1341,1413,1541,4878,13333,61938,133333,141413,
%T A119151 616261,619386,631186,1333333,13333333,133333333,1333333333,
%U A119151 13333333333,133333333333,1279701683121,1333333333333,1959029769461
%N A119151 Numbers k such that the k-th triangular number contains only digits {1,8,9}.
%H A119151 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr189.html">Tridigital Triangular Numbers</a>
%Y A119151 Cf. A000217, A119150. See A119034 for a table of cross-references.
%K A119151 nonn,base
%O A119151 1,2
%A A119151 _Giovanni Resta_, May 10 2006