%I #14 Sep 08 2022 08:46:09
%S 3,5,7,17,257,65537,991172807
%N Primes p such that Product_{d|(p-2)} phi(d) = Product_{d|(p-1)} phi(d) where phi(x) = Euler totient function (A000010).
%C Primes p such that A029940(p-2) = A029940(p-1).
%C First 5 known terms of Fermat primes (A019434) are terms of this sequence.
%C Subsequence of A248796. Supersequence of A247203.
%F A029940(a(n)) = a(n)-1.
%e Prime 17 is in the sequence because A029940(15) = A029940(16) = 64.
%o (Magma) [n: n in [3..100000] | IsPrime(n) and (&*[EulerPhi(d): d in Divisors(n-2)]) eq (&*[EulerPhi(d): d in Divisors(n-1)])]
%Y Cf. A000010, A019434, A029940, A248795, A248796.
%K nonn,more
%O 1,1
%A _Jaroslav Krizek_, Nov 21 2014