%I #3 Mar 31 2012 21:03:28

%S 1,15,21,33,23069,42029,148031,209911

%N Numbers n such that sigma(n)-n = pi(sigma(n)).

%t Do[If[DivisorSigma[1, n]-n==PrimePi[DivisorSigma[1, n]], Print[n]], {n, 1, 10000}]

%K nonn

%O 1,2

%A _Naohiro Nomoto_, Mar 01 2004