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%I #17 Jan 05 2019 01:30:50
%S 3,9,55,65,95,145,155,185,205,2779,2863,21199,174691,174779,1277809,
%T 1301989,1302457,1930091,2554873,8170013,70111213,70111247,514269523,
%U 514269599,27788312339,341964217733,358200797989,763730325367,1975633764583
%N Numbers n such that phi(n) + pi(n) = n+1.
%C a(30) > 2*10^12. - _Giovanni Resta_, Mar 31 2017
%e a(3)= 55: n= 55: phi(n)+pi(n)= 40+16= 56 which equals n+1= 55+1= 56.
%e a(4)= 65: n= 65: phi(n)+pi(n)= 48+18= 66 which equals n+1= 65+1= 66.
%p with(numtheory): KD:= proc() local a,b; a:= n+1; b:=phi(n) +pi(n); if a=b then RETURN (n); fi; end: seq(KD(), n=1..10000000);
%t Do[If [ PrimePi[n]+EulerPhi[n] == n+1, Print[n]], {n,100000000}]
%o (PARI) isok(n) = eulerphi(n)+primepi(n) == n + 1; \\ _Michel Marcus_, Apr 01 2017
%Y Cf. A000203 (sigma(n): sum of divisors of n).
%Y Cf. A000720 (pi(n): number of primes <= n).
%Y Cf. A037170 (numbers n: pi(n) + phi(n)= n).
%K nonn,more
%O 1,1
%A _K. D. Bajpai_, Dec 05 2013
%E a(23)-a(24) from _T. D. Noe_, Dec 05 2013
%E a(25)-a(29) from _Giovanni Resta_, Mar 31 2017
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