A119048 Numbers k such that the k-th triangular number contains only digits {0,1,9}.

1, 4, 13, 19, 44, 141, 195, 199, 424, 1955, 1995, 1999, 14141, 19955, 19995, 19999, 42473, 44741, 47138, 199955, 199995, 199999, 1999955, 1999995, 1999999, 4713620, 19999955, 19999995, 19999999, 199999955, 199999995, 199999999

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• G. Resta, Tridigital Triangular Numbers

Crossrefs

Cf. A000217, A119047. See A119034 for a table of cross-references.

Programs

Magma

[n: n in [1..2*10^7] | Set(Intseq(Binomial(n+1, 2))) subset [0, 1, 9]]; // Vincenzo Librandi, Oct 07 2015

Mathematica

Select[Range[2 10^7], Complement[IntegerDigits[Binomial[# + 1, 2]], {0, 1, 9}] == {}&] (* Vincenzo Librandi, Oct 07 2015 *)
Position[Accumulate[Range[2*10^8]],?(SubsetQ[{0,1,9},IntegerDigits[ #]]&), Heads->False]//Flatten (* _Harvey P. Dale, Dec 01 2018 *)