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

1,2

Comments

Next term exceeds 1.4*10^16.

Links

Table of n, a(n) for n=1..17.

G. Resta, Tridigital Triangular Numbers

Mathematica

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

Prog

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

Crossrefs

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

Sequence in context: A238915 A212680 A027286 * A058851 A167885 A212521

Adjacent sequences: A119041 A119042 A119043 * A119045 A119046 A119047

Keyword

nonn,base,more

Author

Giovanni Resta, May 10 2006

Status

approved