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 A119133 #10 Jul 13 2021 07:28:26
%S A119133 1,3,5,10,11,33,36,101,105,114,333,336,471,1011,1063,1141,1769,3333,
%T A119133 3336,3363,3366,5588,5773,10114,10541,11096,11411,15241,33333,33336,
%U A119133 33363,33366,33663,56773,111010,174101,333333,333336,333363,333366
%N A119133 Numbers k such that the k-th triangular number contains only digits {1,5,6}.
%H A119133 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr156.html">Tridigital Triangular Numbers</a>
%t A119133 (Sqrt[8#+1]-1)/2&/@Select[Flatten[Table[FromDigits/@Tuples[{1,5,6},n],{n,11}]],OddQ[Sqrt[8#+1 ]]&] (* _Harvey P. Dale_, Nov 02 2014 *)
%Y A119133 Cf. A000217, A119132. See A119034 for a table of cross-references.
%K A119133 nonn,base
%O A119133 1,2
%A A119133 _Giovanni Resta_, May 10 2006