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Numbers n such that to phi(n) = pi(n)-1.
3

%I #8 Apr 06 2018 17:40:10

%S 6,12,18,24,42,60

%N Numbers n such that to phi(n) = pi(n)-1.

%e 9 primes below 24 = {2,3,5,7,11,13,17,19,23}; RRS[24]={1,5,7,11,13,17,19,23}, so 24 is here.

%t Do[s=EulerPhi[n]-PrimePi[n]; If[Equal[s, -1], Print[n]], {n, 1, 10000}]

%Y Cf. A037228, A037171, A000010, A000720.

%K fini,full,nonn

%O 1,1

%A _Labos Elemer_, Aug 02 2002