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%I #11 Nov 18 2016 14:03:32
%S 15,45,99,735,1221,1645,1725,1925,2871,4047,8667,13311,16461,19647,
%T 21285,27797,39861,52215,52965,65637,67479,74781,106327,124215,126975,
%U 155511,181917,240397,244839,257951,315695,344175,412863,442417,445215,449493,707859,1362079
%N Composite numbers n such that the sum of proper divisors of n divides 2^n+1.
%C Are all terms odd? There are no even terms < 2*10^12.
%p select(n -> not isprime(n) and 2 &^n + 1 mod (numtheory:-sigma(n)-n) = 0, [$2..10^6]);
%o (PARI) is(n)=n>9 && !isprime(n) && Mod(2,sigma(n)-n)^n==-1 \\ _Charles R Greathouse IV_, Nov 18 2016
%Y Cf. A000051, A001065, A278315.
%K nonn
%O 1,1
%A _Robert Israel_ and _Altug Alkan_, Nov 18 2016
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