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A051280
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n=k/d(k) has exactly 3 solutions, where d(k) = number of divisors of k.
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7
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3, 25, 40, 49, 54, 121, 125, 135, 140, 169, 189, 216, 220, 250, 260, 289, 297, 340, 351, 361, 375, 380, 400, 459, 460, 500, 513, 529, 580, 620, 621, 675, 729, 740, 770, 783, 820, 837, 841, 860, 875, 882, 910, 940, 961, 999, 1060, 1107, 1152, 1161, 1180, 1188, 1190
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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EXAMPLE
| There are exactly 3 numbers k, 9, 18 and 24, with k/d(k)=3.
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MATHEMATICA
| (Select[Table[k / Length @ Divisors[k], {k, 1, 200000}], IntegerQ] // Sort // Split // Select[#, Length[#] == 3 &] &)[[All, 1]][[1 ;; 53]] (* From Jean-François Alcover, Apr 22 2011 *)
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CROSSREFS
| Cf. A033950, A036763, A051278, A051279, A051346.
Sequence in context: A076962 A129599 A042899 * A145609 A120285 A041897
Adjacent sequences: A051277 A051278 A051279 * A051281 A051282 A051283
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KEYWORD
| nonn,easy,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), R. K. Guy, David W. Wilson (davidwwilson(AT)comcast.net)
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