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 A119037 #12 Mar 27 2023 22:36:32
%S A119037 1,10,10011,10440,41041,41001040,141044410,1010004040,4104044101,
%T A119037 14041444410,114011410040100,440404440401100,1041401040044401,
%U A119037 40114114410110140,14001400401400441011,1040410404040110411004140,1014411414040144040404100100
%N A119037 Triangular numbers composed of digits {0,1,4}.
%H A119037 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr014.html">Tridigital Triangular Numbers</a>
%F A119037 a(n) = A000217(A119038(n)). - _Tyler Busby_, Mar 27 2023
%t A119037 Rest[Select[FromDigits/@Tuples[{0, 1, 4}, 12], IntegerQ[(Sqrt[8 # + 1] - 1)/2] &]] (* _Vincenzo Librandi_, Dec 18 2015 *)
%o A119037 (Magma) [t: n in [1..2*10^7] | Set(Intseq(t)) subset {0,1,4} where t is n*(n+1) div 2]; // _Vincenzo Librandi_, Dec 18 2015
%Y A119037 Cf. A000217, A058414, A119038. See A119033 for a table of cross-references.
%K A119037 nonn,base
%O A119037 1,2
%A A119037 _Giovanni Resta_, May 10 2006
%E A119037 a(17) from _Tyler Busby_, Mar 27 2023