A286714 Difference phi(p-1) - phi(p+1) for lesser of twin primes.

-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, 136, 104, 36, 44, 116, 184, 48, 84, 184, 68, 252, 72, 280, 68, 144, 56, 292, 140, 192, 120, 338, 276, 120, 144, 262, 192, 376, 120, 268, 192, 236, 64, 168, 240, 492, 348, 388

Offset: 1

Author

Michel Marcus, May 13 2017

Keywords

• sign

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, A286715.

Programs

Mathematica

(EulerPhi[#-1] - EulerPhi[#+1]) &@ Select[Prime@ Range@ 310, PrimeQ[# + 2] &] (* Giovanni Resta, May 13 2017 *)

PARI

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