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%I #24 Feb 16 2019 01:12:19
%S 3,25,40,49,54,121,125,135,140,169,189,216,220,250,260,289,297,340,
%T 351,361,375,380,400,459,460,500,513,529,580,620,621,675,729,740,770,
%U 783,820,837,841,860,875,882,910,940,961,999,1060,1107,1152,1161,1180,1188,1190
%N Numbers n such that n = k/d(k) has exactly 3 solutions, where d(k) = number of divisors of k.
%C Many terms are of the form a(k) * p^m/(m+1), where p is coprime to the three solutions for k. The sequence of "primitive" terms (i.e. not expressible this way) begins 3, 40, 54, 125, 135, 216, 250.... Are there any such numbers that admit a fourth solution? - _Charlie Neder_, Feb 13 2019
%H T. D. Noe, <a href="/A051280/b051280.txt">Table of n, a(n) for n = 1..1000</a>
%e There are exactly 3 numbers k, 9, 18 and 24, with k/d(k) = 3.
%t (Select[Table[k / Length @ Divisors[k], {k, 1, 200000}], IntegerQ] // Sort // Split // Select[#, Length[#] == 3 &] &)[[All, 1]][[1 ;; 53]] (* _Jean-François Alcover_, Apr 22 2011 *)
%Y Cf. A033950, A036763, A051278, A051279, A051346.
%K nonn,easy,nice
%O 1,1
%A _N. J. A. Sloane_, _R. K. Guy_, _David W. Wilson_