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%I A286715 #9 Sep 11 2019 16:45:46
%S A286715 3,2381,3851,14561,17291,20021,20231,26951,34511,41231,47741,50051,
%T A286715 52361,55931,57191,65171,67211,67271,70841,82811,87011,98561,101501,
%U A286715 101531,108461,117041,119771,126491,129221,134681,136991,142871,145601,150221,156941,165551,166601
%N A286715 Lesser of twin primes for which phi(p-1) < phi(p+1).
%H A286715 Amiram Eldar, <a href="/A286715/b286715.txt">Table of n, a(n) for n = 1..10000</a>
%H A286715 Stephan Ramon Garcia, Elvis Kahoro, Florian Luca, <a href="https://arxiv.org/abs/1705.02485">Primitive root discrepancy for twin primes</a>, arXiv:1705.02485 [math.NT], 2017.
%t A286715 s = {}; p = 3; Do[q = NextPrime[p]; If[q - p != 2, p = q; Continue[]]; If[EulerPhi[p + 1] > EulerPhi[p - 1], AppendTo[s, p]]; p = q, {15500}]; s (* _Amiram Eldar_, Sep 11 2019 *)
%o A286715 (PARI) lista(nn) = forprime(p=2, nn, if (isprime(p+2) && (eulerphi(p-1) < eulerphi(p+1)), print1(p, ", ")));
%Y A286715 Cf. A001359, A006512, A008330, A286714.
%K A286715 nonn
%O A286715 1,1
%A A286715 _Michel Marcus_, May 13 2017

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