cp's OEIS Frontend

A072326 Conjectured values of n such that the sum of proper divisors of x*n is never prime for any x >= 1 (i.e., sigma(xn) - xn is never prime for x >= 1).

%I A072326 #16 Aug 01 2017 08:04:07
%S A072326 42,78,84,114,126,156,168,174,186,210
%N A072326 Conjectured values of n such that the sum of proper divisors of x*n is never prime for any x >= 1 (i.e., sigma(xn) - xn is never prime for x >= 1).
%C A072326 From _Michel Marcus_, Jul 31 2017: (Start)
%C A072326 None of the given terms are correct.
%C A072326 For each term, here are some x such that sigma(n*x) - n*x is prime.
%C A072326 42, x: 5145000, 6923112, 7408800,
%C A072326 78, x: 26693550, 30371328,
%C A072326 114, x: 370386,
%C A072326 126, x: 1715000, 2307704, 2469600, 4390400, 5556600, 6860000,
%C A072326 156, x: 13346775, 15185664,
%C A072326 168, x: 1286250, 1730778, 1852200, 3292800, 4167450, 5145000,
%C A072326 174, x: 17400, 69600, 156600, 178176, 336864, 368184, 400896, 585336,
%C A072326 186, x: 2859936,
%C A072326 210, x: 1029000, 1481760, 2634240, 3333960, 4116000,
%C A072326 (End)
%K A072326 dead
%O A072326 1,1
%A A072326 _Benoit Cloitre_, Jul 31 2002