A060660 - OEIS

%I #2 Mar 30 2012 17:30:31

%S 96,120,180,312,372,420,434,456,540,546,560,624,702,728,798,816,930,

%T 1064,1120,1170,1404,1632,1638,1674,1710,1776,1792,1944,2100,2240,

%U 2544,2560,2664,2760,2800,2844,2856,2940,2952,3000,3040,3048,3060,3080,3096

%N Sigma(x) = n has exactly four solutions.

%e 96 = sigma(42) = sigma(62) = sigma(69) = sigma(77).

%t a = Table[ 0, {5000} ]; Do[ s = DivisorSigma[ 1, n ]; If[ s < 5001, a[ [ s ] ]++ ], {n, 1, 5000} ]; Select[ Range[ 5000 ], a[ [ # ] ] == 4 & ]

%Y Cf. A007370, A007371, A007372.

%K nonn

%O 1,1

%A _Robert G. Wilson v_, Apr 18 2001