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Difference phi(p-1) - phi(p+1) for lesser of twin primes.
4

%I #11 Sep 11 2019 15:50:55

%S -1,0,0,2,4,4,12,0,8,16,20,32,40,8,24,40,32,60,4,24,60,84,24,56,24,

%T 136,104,36,44,116,184,48,84,184,68,252,72,280,68,144,56,292,140,192,

%U 120,338,276,120,144,262,192,376,120,268,192,236,64,168,240,492,348,388

%N Difference phi(p-1) - phi(p+1) for lesser of twin primes.

%H Amiram Eldar, <a href="/A286714/b286714.txt">Table of n, a(n) for n = 1..10000</a>

%H 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 (EulerPhi[#-1] - EulerPhi[#+1]) &@ Select[Prime@ Range@ 310, PrimeQ[# + 2] &] (* _Giovanni Resta_, May 13 2017 *)

%o (PARI) lista(nn) = forprime(p=2, nn, if (isprime(p+2), print1(eulerphi(p-1)-eulerphi(p+1), ", ")));

%Y Cf. A001359, A006512, A008330, A286715.

%K sign

%O 1,4

%A _Michel Marcus_, May 13 2017