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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
OFFSET
0,2
LINKS
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
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Apr 08 2002
EXTENSIONS
Edited and extended by Robert G. Wilson v, Apr 12 2002
STATUS
approved