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 A119041 #10 Mar 27 2023 22:36:36
%S A119041 1,6,10,66,666,10011,16110,66066,600060,6601161,10006101,11066160,
%T A119041 660061611,1001661661,1061660160,1100016060,1660061010,1001000010660,
%U A119041 1066006600011,10010000160006,106001000601616,60660116660011611,1660616006066010601060060
%N A119041 Triangular numbers composed of digits {0,1,6}.
%H A119041 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr016.html">Tridigital Triangular Numbers</a>
%F A119041 a(n) = A000217(A119042(n)). - _Tyler Busby_, Mar 27 2023
%t A119041 Rest[Select[FromDigits/@Tuples[{0,1,6},17],OddQ[Sqrt[8#+1]]&]] (* _Harvey P. Dale_, Jan 14 2017 *)
%Y A119041 Cf. A000217, A058418, A119042. See A119033 for a table of cross-references.
%K A119041 nonn,base
%O A119041 1,2
%A A119041 _Giovanni Resta_, May 10 2006
%E A119041 a(23) from _Tyler Busby_, Mar 27 2023