A050759 Numbers k such that the decimal expansion of (k^2 + k)/2 (the k-th triangular number) contains no pair of consecutive equal digits.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 37, 38, 39, 40, 41, 42, 43, 45, 46, 50, 51, 52, 53, 54, 55, 56, 57, 60, 61, 62, 63, 64, 65, 68, 69, 70, 72, 73, 75, 76, 78, 79, 80, 82, 83, 84, 86, 87, 88

Offset

1,3

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

filter:= proc(n) local t;
  t:= convert(n*(n+1)/2, base, 10);
  not member(0, t[2..-1]-t[1..-2])
end proc:
select(filter, [$0..100]); # Robert Israel, Oct 14 2024

Mathematica

Select[Range[0, 88], FreeQ[Differences[IntegerDigits[(#^2+#)/2]], 0]&] (* Jayanta Basu, May 31 2013 *)

Crossrefs

Cf. A043096, A000217, A050760.

Sequence in context: A118766 A136399 A056167 * A039274 A102487 A343951

Adjacent sequences: A050756 A050757 A050758 * A050760 A050761 A050762

Keyword

nonn,base

Author

Patrick De Geest, Sep 15 1999

Extensions

Name clarified and offset changed to 1 by Jon E. Schoenfield, Oct 16 2019

Status

approved