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%I #13 Mar 28 2023 17:07:43
%S 6,55,66,666,5565,6555,5656566,5676765,6655776,56567566,575675766555,
%T 677767555675,555665666566566,555667666766556,5755656755766655,
%U 565767676566675765,7557657566575767666,5555555666655656666556566566566
%N Triangular numbers composed of digits {5,6,7}.
%C a(19) > 10^40. - _Tyler Busby_, Mar 28 2023
%H Giovanni Resta, <a href="http://www.numbersaplenty.com/tr/tr567.html">Tridigital Triangular Numbers</a>.
%F a(n) = A000217(A119219(n)). - _Michel Marcus_, Mar 27 2023
%Y Cf. A000217, A053969, A119219. See A119033 for a table of cross-references.
%K nonn,base
%O 1,1
%A _Giovanni Resta_, May 10 2006
%E a(18) from _Tyler Busby_, Mar 28 2023
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