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 A119052 #12 Sep 08 2022 08:45:25
%S A119052 10,100,224,714,1000,10000,32410,67089,100000,210010,1000000,1019825,
%T A119052 2100010,2109599,3231100,10000000,21000010,33173785,71450010,
%U A119052 100000000,200101000,201000100,210000010,663702049,1000000000
%N A119052 Numbers k such that the k-th triangular number contains only digits {0,2,5}.
%H A119052 G. Resta, <a href="http://www.numbersaplenty.com/tr/tr025.html">Tridigital Triangular Numbers</a>
%t A119052 Select[Range[2 10^7], Complement[IntegerDigits[Binomial[# + 1, 2]], {0, 2, 5}] == {}&] (* _Vincenzo Librandi_, Oct 07 2015 *)
%o A119052 (Magma) [n: n in [1..2*10^7] | Set(Intseq(Binomial(n+1, 2))) subset [0, 2, 5]]; // _Vincenzo Librandi_, Oct 07 2015
%Y A119052 Cf. A000217, A119051. See A119034 for a table of cross-references.
%K A119052 nonn,base
%O A119052 1,1
%A A119052 _Giovanni Resta_, May 10 2006