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A234848 Triangular numbers with digits in nondecreasing order. 1

%I

%S 0,1,3,6,15,28,36,45,55,66,78,136,378,666,1128,1225,1378,2278,2346,

%T 2556,5778,12246,13366,22366,22578,35778,111156,222778,223446,333336,

%U 1113778,1222266,1457778,2235555,3557778,22227778,22234446,111116778,156777778,222446778

%N Triangular numbers with digits in nondecreasing order.

%C 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

%H T. D. Noe, <a href="/A234848/b234848.txt">Table of n, a(n) for n = 1..328</a> (terms less than 10^200)

%t 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 *)

%Y Cf. A000217, A028820.

%K base,nonn

%O 1,3

%A _Zak Seidov_, Dec 31 2013

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Last modified August 9 20:09 EDT 2020. Contains 336326 sequences. (Running on oeis4.)