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Numbers k such that the k-th triangular number contains only digits {0,4,7}.
2

%I #11 Jul 13 2021 07:24:02

%S 284,3080,97680,9460126854061817544

%N Numbers k such that the k-th triangular number contains only digits {0,4,7}.

%C No other terms below 1.4*10^20.

%H G. Resta, <a href="http://www.numbersaplenty.com/tr/tr047.html">Tridigital Triangular Numbers</a>

%Y Cf. A000217, A218399. See A119034 for a table of cross-references.

%K base,nonn,more

%O 1,1

%A _Max Alekseyev_, Oct 28 2012