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A068149 Triangular numbers in which neighboring digits differ at most by 1. Allowed neighbors of 9 are 0, 8 and 9. 0
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified August 10 00:32 EDT 2022. Contains 356026 sequences. (Running on oeis4.)