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%I #16 Mar 27 2023 01:29:00
%S 78,8778,448878,887778,7478778,88877778,8888777778,44847878778,
%T 747488474778,888887777778,88888877777778,8888888777777778,
%U 888888887777777778,7778777484477877878,88888888877777777778,7444484774887874784778,8888888888777777777778
%N Triangular numbers composed of digits {4,7,8}.
%H Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr478.html">Tridigital Triangular Numbers</a>.
%F a(n) = A000217(A119217(n)). - _Tyler Busby_, Mar 26 2023
%t Table[Select[FromDigits/@Tuples[{4,7,8},n],OddQ[Sqrt[8#+1]]&],{n,20}]//Flatten (* The program will take a long time to run. *) (* _Harvey P. Dale_, Oct 15 2017 *)
%Y Cf. A000217, A053963, A119217. See A119033 for a table of cross-references.
%K nonn,base
%O 1,1
%A _Giovanni Resta_, May 10 2006
%E a(16)-a(17) from _Tyler Busby_, Mar 26 2023
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