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A234848 Triangular numbers with digits in nondecreasing order. 1
0, 1, 3, 6, 15, 28, 36, 45, 55, 66, 78, 136, 378, 666, 1128, 1225, 1378, 2278, 2346, 2556, 5778, 12246, 13366, 22366, 22578, 35778, 111156, 222778, 223446, 333336, 1113778, 1222266, 1457778, 2235555, 3557778, 22227778, 22234446, 111116778, 156777778, 222446778 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Beyond 222446778, all terms are k(k+1)/2 for k = 2s7, 6s7, or 6s8, where s stands for any number of 6's. - T. D. Noe, Jan 01 2014

LINKS

T. D. Noe, Table of n, a(n) for n = 1..328 (terms less than 10^200)

MATHEMATICA

inOrder[nums_] := Min[Differences[nums]] >= 0; t = {}; Do[tri = n*(n+1)/2; If[inOrder[IntegerDigits[tri]], AppendTo[t, tri]], {n, 0, 10^5}]; t (* T. D. Noe, Dec 31 2013 *)

CROSSREFS

Cf. A000217, A028820.

Sequence in context: A056278 A000740 A161625 * A300761 A069712 A076971

Adjacent sequences:  A234845 A234846 A234847 * A234849 A234850 A234851

KEYWORD

base,nonn

AUTHOR

Zak Seidov, Dec 31 2013

STATUS

approved

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Last modified July 13 07:30 EDT 2020. Contains 335676 sequences. (Running on oeis4.)