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 A119136 #10 Mar 24 2023 03:03:00
%S A119136 1,15,55,5151,8515,581581,885115,1188111,11188815,51151555,81581151,
%T A119136 88851115,851585815,8888511115,888885111115,88888851111115,
%U A119136 8888888511111115,888888885111111115,5885188811851888815,15158585181118581555,88888888851111111115
%N A119136 Triangular numbers composed of digits {1,5,8}.
%H A119136 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr158.html">Tridigital Triangular Numbers</a>
%F A119136 a(n) = A000217(A119137(n)). - _Michel Marcus_, Mar 24 2023
%Y A119136 Cf. A000217, A053905, A119137. See A119033 for a table of cross-references.
%K A119136 nonn,base
%O A119136 1,2
%A A119136 _Giovanni Resta_, May 10 2006
%E A119136 a(20)-a(21) from _Tyler Busby_, Mar 23 2023