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 A119135 #11 Sep 08 2022 08:45:25
%S A119135 1,5,10,18,58,101,149,1050,1885,5925,10114,15173,47226,550594,585005,
%T A119135 1049925,1533085,56174285,104987349,123053789,1017425330,1230586669,
%U A119135 1245114914,38878044589,101111538130,177627538130,4728038741701
%N A119135 Numbers k such that the k-th triangular number contains only digits {1,5,7}.
%H A119135 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr157.html">Tridigital Triangular Numbers</a>
%t A119135 Select[Range[2 10^7], Complement[IntegerDigits[Binomial[# + 1, 2]], {1, 5, 7}] == {}&] (* _Vincenzo Librandi_, Oct 07 2015 *)
%o A119135 (Magma) [n: n in [1..2*10^7] | Set(Intseq(Binomial(n+1, 2))) subset [1, 5, 7]]; // _Vincenzo Librandi_, Oct 07 2015
%Y A119135 Cf. A000217, A119134. See A119034 for a table of cross-references.
%K A119135 nonn,base
%O A119135 1,2
%A A119135 _Giovanni Resta_, May 10 2006