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%I #15 Sep 08 2022 08:45:25
%S 1,4,13,19,44,141,195,199,424,1955,1995,1999,14141,19955,19995,19999,
%T 42473,44741,47138,199955,199995,199999,1999955,1999995,1999999,
%U 4713620,19999955,19999995,19999999,199999955,199999995,199999999
%N Numbers k such that the k-th triangular number contains only digits {0,1,9}.
%H G. Resta, <a href="http://www.numbersaplenty.com/tr/tr019.html">Tridigital Triangular Numbers</a>
%t Select[Range[2 10^7], Complement[IntegerDigits[Binomial[# + 1, 2]], {0, 1, 9}] == {}&] (* _Vincenzo Librandi_, Oct 07 2015 *)
%t Position[Accumulate[Range[2*10^8]],_?(SubsetQ[{0,1,9},IntegerDigits[ #]]&), Heads->False]//Flatten (* _Harvey P. Dale_, Dec 01 2018 *)
%o (Magma) [n: n in [1..2*10^7] | Set(Intseq(Binomial(n+1, 2))) subset [0, 1, 9]]; // _Vincenzo Librandi_, Oct 07 2015
%Y Cf. A000217, A119047. See A119034 for a table of cross-references.
%K nonn,base
%O 1,2
%A _Giovanni Resta_, May 10 2006
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