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 A119156 #18 Mar 30 2023 20:56:09
%S A119156 3,28,3828,828828,388333828828,223832333328828,332828222833288828828,
%T A119156 28388332838238232223328828
%N A119156 Triangular numbers composed of digits {2,3,8}.
%C A119156 a(9) > 10^45. - _Tyler Busby_, Mar 29 2023
%H A119156 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr238.html">Tridigital Triangular Numbers</a>.
%F A119156 a(n) = A000217(A119157(n)). - _Tyler Busby_, Mar 29 2023
%o A119156 (Python)
%o A119156 klimit = 10**6
%o A119156 A000217 = (k*(k+1)//2 for k in range(klimit)) # generator
%o A119156 print([m for m in A000217 if set(str(m)) <= set("238")]) # _Michael S. Branicky_, Mar 28 2021
%Y A119156 Cf. A000217, A119157. See A119033 for a table of cross-references.
%K A119156 nonn,base,more
%O A119156 1,1
%A A119156 _Giovanni Resta_, May 10 2006