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 A069712 Triangular numbers with arithmetic mean of digits = integer (sum of digits = A multiple of the number of digits). 4
 1, 3, 6, 15, 28, 55, 66, 91, 105, 120, 153, 171, 210, 231, 276, 300, 351, 378, 435, 465, 528, 561, 630, 666, 741, 780, 861, 903, 990, 1128, 1326, 1830, 2145, 2415, 3081, 5151, 5995, 6105, 7140, 8385, 8646, 9591, 9870, 10153, 11026, 11175, 12246, 12403 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Harvey P. Dale, Table of n, a(n) for n = 0..1000 MATHEMATICA Do[ If[ IntegerQ[ Apply[ Plus, IntegerDigits[n(n + 1)/2]] / Floor[ Log[10, n(n + 1)/2] + 1]], Print[n(n + 1)/2]], {n, 1, 10^3}] Select[Accumulate[Range[200]], IntegerQ[Mean[IntegerDigits[#]]]&] (* Harvey P. Dale, Jun 17 2017 *) CROSSREFS Cf. A069709, A069710, A069711. Sequence in context: A161625 A234848 A300761 * A076971 A103529 A185378 Adjacent sequences:  A069709 A069710 A069711 * A069713 A069714 A069715 KEYWORD base,nonn AUTHOR Amarnath Murthy, Apr 08 2002 EXTENSIONS Edited and extended by Robert G. Wilson v, Apr 12 2002 STATUS approved

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Last modified August 3 13:49 EDT 2020. Contains 336198 sequences. (Running on oeis4.)