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%I A115919 #11 Jul 15 2021 21:25:40
%S A115919 2,3,4,5,7,8,9,11,13,16,17,19,23,25,29,31,32,36,37,41,43,47,50,53,59,
%T A115919 61,67,71,73,79,81,83,89,97,101,103,107,109,113,121,127,128,131,137,
%U A115919 139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,225,227
%N A115919 Numbers k such that sigma(k) - phi(k) is a prime number.
%H A115919 Charles R Greathouse IV, <a href="/A115919/b115919.txt">Table of n, a(n) for n = 1..10000</a>
%e A115919 sigma(81) - phi(81) = 67, a prime.
%t A115919 Select[Range[300],PrimeQ[DivisorSigma[1,#]-EulerPhi[#]]&]  (* _Harvey P. Dale_, Feb 25 2011 *)
%o A115919 (PARI) is(n)=isprime(sigma(n)-eulerphi(n)) \\ _Charles R Greathouse IV_, Nov 27 2013
%Y A115919 Cf. A038344.
%K A115919 nonn
%O A115919 1,1
%A A115919 _Giovanni Resta_, Feb 06 2006

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