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%I #10 Mar 29 2017 09:59:14
%S 1,4,8,27,35,215,235,2611,65113,174647,1301317,1302509,5021647,
%T 10885081,36319939,70112131,70113559,325575773,514258883,742327529,
%U 1069238453,18721771909,27788563039,113350570453,835005036247
%N Numbers n such that n is the phi(n)-th nonprime number.
%C n is in the sequence iff n is't prime and n=phi(n)+pi(n). This sequence is a subsequence of A037170 and 2 is the only term of A037170 which is not in this sequence because 2 is the only prime p such that p=phi(p)+pi(p).
%C There is no further term up to 10^9. - _Farideh Firoozbakht_, Jul 26 2009
%C a(24) > 10^11. - _Donovan Johnson_, Feb 05 2010
%C a(26) > 2.3*10^12. - _Giovanni Resta_, Mar 28 2017
%e 27 is in the sequence because phi(27)=18 and 27 is the 18th nonprime number, the first 17 nonprime numbers are 1,4,6,8,9,10,12,14,15,16,18,20,21,22,24,25 & 26.
%t Select[Range[10^5], # == PrimePi[#] + EulerPhi[#] && ! PrimeQ[#] &] (* _Giovanni Resta_, Mar 28 2017 *)
%Y Cf. A037170, A100410, A018252.
%K more,nonn
%O 1,2
%A _Farideh Firoozbakht_, Dec 01 2004
%E a(19)-a(20) from _Farideh Firoozbakht_, Jul 26 2009
%E a(21)-a(23) from _Donovan Johnson_, Feb 05 2010
%E a(24)-a(25) from _Giovanni Resta_, Mar 28 2017
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