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 A119087 #11 Mar 31 2023 14:12:53
%S A119087 6,66,666,6670,66066,600060,67007676,670677000,66067760760,
%T A119087 76666077676,76670776666,660067006660776,7600067000007076,
%U A119087 6700677067067607000,60660060606000770770776700,776600760606070666600067770,7766770606766667760666707766
%N A119087 Triangular numbers composed of digits {0,6,7}.
%H A119087 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr067.html">Tridigital Triangular Numbers</a>.
%F A119087 a(n) = A000217(A119088(n)). - _Tyler Busby_, Mar 31 2023
%Y A119087 Cf. A000217, A058450, A119088. See A119033 for a table of cross-references.
%K A119087 nonn,base
%O A119087 1,1
%A A119087 _Giovanni Resta_, May 10 2006
%E A119087 a(16)-a(17) from _Tyler Busby_, Mar 23 2023