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

1,2

Links

Table of n, a(n) for n=1..27.

G. Resta, Tridigital Triangular Numbers

Mathematica

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

Prog

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

Crossrefs

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

Sequence in context: A296552 A251928 A153370 * A083287 A091922 A030776

Adjacent sequences: A119132 A119133 A119134 * A119136 A119137 A119138

Keyword

nonn,base

Author

Giovanni Resta, May 10 2006

Status

approved