%I #17 Jul 13 2021 07:24:17
%S 44,426096444,12641976109035254775
%N Numbers k such that the k-th triangular number contains only digits {0,7,9}.
%C No other terms below 1.4*10^20.
%H G. Resta, <a href="http://www.numbersaplenty.com/tr/tr079.html">Tridigital Triangular Numbers</a>
%Y Cf. A000217, A218401. See A119034 for a table of cross-references.
%K base,nonn,more,hard,bref
%O 1,1
%A _Max Alekseyev_, Oct 28 2012