A286715 Lesser of twin primes for which phi(p-1) < phi(p+1).

3, 2381, 3851, 14561, 17291, 20021, 20231, 26951, 34511, 41231, 47741, 50051, 52361, 55931, 57191, 65171, 67211, 67271, 70841, 82811, 87011, 98561, 101501, 101531, 108461, 117041, 119771, 126491, 129221, 134681, 136991, 142871, 145601, 150221, 156941, 165551, 166601

Offset: 1

Author

Michel Marcus, May 13 2017

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Stephan Ramon Garcia, Elvis Kahoro, Florian Luca, Primitive root discrepancy for twin primes, arXiv:1705.02485 [math.NT], 2017.

Crossrefs

Cf. A001359, A006512, A008330, A286714.

Programs

Mathematica

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 *)

PARI

lista(nn) = forprime(p=2, nn, if (isprime(p+2) && (eulerphi(p-1) < eulerphi(p+1)), print1(p, ", ")));