A068149 Triangular numbers in which neighboring digits differ at most by 1. Allowed neighbors of 9 are 0, 8 and 9.

0, 1, 3, 6, 10, 21, 45, 55, 66, 78, 210, 666, 990, 2211, 3321, 5565, 6555, 8778, 10011, 90100, 112101, 222111, 232221, 443211, 887778, 5433456, 5456556, 5656566, 5676765, 22221111, 22321221, 34565455, 88877778, 211099878, 212210901

Offset

0,3

Links

Table of n, a(n) for n=0..34.

Mathematica

Do[a = IntegerDigits[n(n + 1)/2]; k = 1; l = Length[a]; While[k < l && (Abs[a[[k]]- a[[k + 1]]] < 2 || Abs[a[[k]] - a[[k + 1]]] > 8), k++ ]; If[k == l, Print[n(n + 1)/2]], {n, 0, 10^5} ]
Select[Accumulate[Range[0, 30000]], Max[Select[Abs[Differences[ IntegerDigits[ #]]], #!=9&]]<2&] (* Harvey P. Dale, Oct 09 2013 *)

Crossrefs

Cf. A000217.

Sequence in context: A027671 A167617 A274018 * A068709 A068804 A117834

Adjacent sequences: A068146 A068147 A068148 * A068150 A068151 A068152

Keyword

base,easy,nonn

Author

Amarnath Murthy, Feb 23 2002

Extensions

Edited and extended by Robert G. Wilson v and Sascha Kurz, Mar 01 2002

Status

approved