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 A119154 #10 Mar 28 2023 12:40:49
%S A119154 3,6,36,66,666,22366,333336,23232336,336662326,2232222336,3263633236,
%T A119154 6266233326,262322266326,266633626626,2263263223266,36226633633326,
%U A119154 66333362366236266,3236622262232626626666,3322222636222323322336,2332636666226262326336266
%N A119154 Triangular numbers composed of digits {2,3,6}.
%H A119154 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr236.html">Tridigital Triangular Numbers</a>.
%F A119154 a(n) = A000217(A119155(n)). - _Tyler Busby_, Mar 28 2023
%t A119154 Select[Flatten[Table[FromDigits/@Tuples[{2,3,6},n],{n,10}]],OddQ[Sqrt[8#+1]]&] (* The program generates the first 12 terms of the sequence. To generate more, increase the constant after "n," but the program will take longer to run. *) (* _Harvey P. Dale_, Apr 18 2020 *)
%Y A119154 Cf. A000217, A058458, A119155. See A119033 for a table of cross-references.
%K A119154 nonn,base
%O A119154 1,1
%A A119154 _Giovanni Resta_, May 10 2006
%E A119154 a(20) from _Tyler Busby_, Mar 28 2023