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 A119048 #15 Sep 08 2022 08:45:25
%S A119048 1,4,13,19,44,141,195,199,424,1955,1995,1999,14141,19955,19995,19999,
%T A119048 42473,44741,47138,199955,199995,199999,1999955,1999995,1999999,
%U A119048 4713620,19999955,19999995,19999999,199999955,199999995,199999999
%N A119048 Numbers k such that the k-th triangular number contains only digits {0,1,9}.
%H A119048 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr019.html">Tridigital Triangular Numbers</a>
%t A119048 Select[Range[2 10^7], Complement[IntegerDigits[Binomial[# + 1, 2]], {0, 1, 9}] == {}&] (* _Vincenzo Librandi_, Oct 07 2015 *)
%t A119048 Position[Accumulate[Range[2*10^8]],_?(SubsetQ[{0,1,9},IntegerDigits[ #]]&), Heads->False]//Flatten (* _Harvey P. Dale_, Dec 01 2018 *)
%o A119048 (Magma) [n: n in [1..2*10^7] | Set(Intseq(Binomial(n+1, 2))) subset [0, 1, 9]]; // _Vincenzo Librandi_, Oct 07 2015
%Y A119048 Cf. A000217, A119047. See A119034 for a table of cross-references.
%K A119048 nonn,base
%O A119048 1,2
%A A119048 _Giovanni Resta_, May 10 2006