A116544 Triangular numbers for which the multiplicative digital root is also a triangular number.

0, 1, 3, 6, 10, 28, 45, 55, 78, 105, 120, 190, 210, 231, 253, 276, 300, 325, 378, 406, 435, 465, 528, 561, 595, 630, 703, 741, 780, 820, 861, 903, 990, 1035, 1081, 1128, 1225, 1275, 1378, 1485, 1540, 1596, 1653, 1770, 1830, 2016, 2080, 2145, 2278, 2346, 2415

Offset

1,3

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

a = {}; For[n = 0, n < 100, n++, b = n*(n + 1)/2; While[b > 9, b = Times @@ IntegerDigits[b]]; If[Length[Intersection[{b}, {0, 1, 3, 6}]] == 1, AppendTo[a, n*(n + 1)/2]]]; a (* Stefan Steinerberger, Jan 02 2008 *)
dr[n_]:=NestWhile[Times@@IntegerDigits[#]&, n, #>9&]; With[{trnos= Accumulate[Range[0, 80]]}, Select[trnos, MemberQ[trnos, dr[#]]&]] (* Harvey P. Dale, Nov 02 2011 *)

Crossrefs

Sequence in context: A068818 A068866 A137173 * A110891 A197435 A240514

Adjacent sequences: A116541 A116542 A116543 * A116545 A116546 A116547

Keyword

nonn,base

Author

Luc Stevens (lms022(AT)yahoo.com), Apr 03 2006

Extensions

More terms from Stefan Steinerberger, Jan 02 2008

Status

approved