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 A119204 #14 Mar 28 2023 15:08:37
%S A119204 45,55,5747745,744574755,77545447574475,4745745457757444544544575,
%T A119204 44477447457545755547775754555,547457575775574544754447747777455
%N A119204 Triangular numbers composed of digits {4,5,7}.
%C A119204 a(8) > 10^40. - _Tyler Busby_, Mar 28 2023
%H A119204 Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr457.html">Tridigital Triangular Numbers</a>.
%F A119204 a(n) = A000217(A119205(n)). - _Jon E. Schoenfield_, Mar 27 2023
%Y A119204 Cf. A000217, A053951, A119205. See A119033 for a table of cross-references.
%K A119204 nonn,base,more
%O A119204 1,1
%A A119204 _Giovanni Resta_, May 10 2006
%E A119204 a(8) from _Tyler Busby_, Mar 28 2023