The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A116544 Triangular numbers for which the multiplicative digital root is also a triangular number. 1
 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 (list; graph; refs; listen; history; text; internal format)
 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: A302094 A068818 A137173 * A068866 A110891 A197435 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 5 19:30 EDT 2020. Contains 336213 sequences. (Running on oeis4.)