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A116544
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Triangular numbers for which the multiplicative digital root is also a triangular number.
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1
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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; internal format)
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OFFSET
| 1,3
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LINKS
| Harvey P. Dale, Table of n, a(n) for n = 1..1000
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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 (stefan.steinerberger(AT)gmail.com), Jan 02 2008
dr[n_]:=NestWhile[Times@@IntegerDigits[#]&, n, #>9&]; With[{trnos= Accumulate[Range[0, 80]]}, Select[trnos, MemberQ[trnos, dr[#]]&]] (* From Harvey P. Dale, Nov 02 2011 *)
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CROSSREFS
| Sequence in context: A048006 A068818 A137173 * A068866 A110891 A197435
Adjacent sequences: A116541 A116542 A116543 * A116545 A116546 A116547
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KEYWORD
| nonn,base
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AUTHOR
| Luc Stevens (lms022(AT)yahoo.com), Apr 03 2006
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EXTENSIONS
| More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Jan 02 2008
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