A069712 - OEIS

A069712

Triangular numbers with arithmetic mean of digits = integer (sum of digits = A multiple of the number of digits).

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