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Numbers k such that the k-th triangular number contains only digits {0,4,9}.
2

%I #8 Jul 13 2021 01:25:25

%S 44,2831780,1407437419,140715344155

%N Numbers k such that the k-th triangular number contains only digits {0,4,9}.

%C Next term exceeds 1.4*10^16.

%H G. Resta, <a href="http://www.numbersaplenty.com/tr/tr049.html">Tridigital Triangular Numbers</a>

%Y Cf. A000217, A119077. See A119034 for a table of cross-references.

%K nonn,base,more

%O 1,1

%A _Giovanni Resta_, May 10 2006