login

Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.

Numbers n such that n=prime(phi(sigma(pi(n)))).
1

%I #2 Mar 30 2012 17:37:48

%S 2,3,19,37,719,1511,5443,69709,386093,1907819,10777931,17819101,

%T 18653749,56125547,60163267,98911811,272887613,567611663,989060309,

%U 2444540149

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

%C It is obvious that all terms are primes. There is no further term up to 5*10^9.

%t Do[If[n=Prime[m];m==EulerPhi[DivisorSigma[1,PrimePi[n]]],Print[n]],{m,235000000}]

%Y Cf. A000010, A000040, A000720, A000203, A163666.

%K more,nonn

%O 1,1

%A _Farideh Firoozbakht_, Aug 04 2009