A119135 Numbers k such that the k-th triangular number contains only digits {1,5,7}.

1, 5, 10, 18, 58, 101, 149, 1050, 1885, 5925, 10114, 15173, 47226, 550594, 585005, 1049925, 1533085, 56174285, 104987349, 123053789, 1017425330, 1230586669, 1245114914, 38878044589, 101111538130, 177627538130, 4728038741701

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• G. Resta, Tridigital Triangular Numbers

Crossrefs

Cf. A000217, A119134. See A119034 for a table of cross-references.

Programs

Magma

[n: n in [1..2*10^7] | Set(Intseq(Binomial(n+1, 2))) subset [1, 5, 7]]; // Vincenzo Librandi, Oct 07 2015

Mathematica

Select[Range[2 10^7], Complement[IntegerDigits[Binomial[# + 1, 2]], {1, 5, 7}] == {}&] (* Vincenzo Librandi, Oct 07 2015 *)