%I #27 Sep 08 2022 08:46:16

%S 2,3,5,17,37,101,257,401,577,1297,1601,2917,4357,8101,8837,12101,

%T 13457,14401,22501,25601,28901,30977,32401,33857,41617,52901,55697,

%U 57601,62501,65537,69697,72901,80657,90001,93637,115601,147457,160001,193601,217157,220901

%N Primes p such that gcd(phi(p-1), sigma(p-1)) = 1 with phi = A000010, sigma = A000203.

%C Fermat primes (A019434) are terms.

%H Jaroslav Krizek, <a href="/A270539/b270539.txt">Table of n, a(n) for n = 1..200</a>

%e Prime 17 is a term because gcd(sigma(16), phi(16)) = gcd(31, 8) = 1.

%o (Magma) [n: n in [1..10^6] | IsPrime(n) and GCD(SumOfDivisors(n-1), EulerPhi(n-1)) eq 1]

%o (PARI) isok(p) = isprime(p) && (gcd(eulerphi(p-1), sigma(p-1)) == 1); \\ _Michel Marcus_, Oct 06 2021

%Y Cf. A000010, A000203, A019434.

%K nonn

%O 1,1

%A _Jaroslav Krizek_, Jul 12 2016