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 A068473 Numbers n such that phi((prime(n)+1)/2)=sigma(n). 1

%I

%S 31,51,77,87,158,184,297,308,573,621,766,786,799,826,1167,1330,1946,

%T 2030,2280,3058,3213,5015,5093,5271,5374,8307,8813,9730,10364,10557,

%U 11229,12750,13462,14145,15807,20606,23115,24633,24795,26400,28015

%N Numbers n such that phi((prime(n)+1)/2)=sigma(n).

%H Harvey P. Dale, <a href="/A068473/b068473.txt">Table of n, a(n) for n = 1..100</a>

%t Select[Range[2,30000],EulerPhi[(Prime[#]+1)/2]==DivisorSigma[1,#]&] (* _Harvey P. Dale_, May 01 2015 *)

%o (PARI) for(n=2,45000, if(eulerphi((prime(n)+1)/2)==sigma(n),print1(n,",")))

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Mar 10 2002

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Last modified December 5 17:28 EST 2021. Contains 349557 sequences. (Running on oeis4.)