A119044 Numbers k such that the k-th triangular number contains only digits {0,1,7}.

1, 4, 18, 58, 59, 141, 471418, 185310604, 451023506, 1184061400, 1844511706, 4474395400, 14266749459, 18444896915, 48521543066, 11838218371106, 39270880053981

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base
• more

Comments

Next term exceeds 1.4*10^16.

Links

• G. Resta, Tridigital Triangular Numbers

Crossrefs

Cf. A000217, A119043. See A119034 for a table of cross-references.

Programs

Magma

[n: n in [1..2*10^7] | Set(Intseq(Binomial(n+1,2))) subset [0,1,7]]; // Vincenzo Librandi, Oct 06 2015

Mathematica

Select[Range[3 10^7], Complement[IntegerDigits[Binomial[# + 1, 2]], {0, 1, 7}] == {} &] (* Vincenzo Librandi, Oct 06 2015 *)