This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A247164 #21 Jul 27 2025 10:35:14
%S A247164 3,5,7,17,257,65537,991172807,1872619667,4081364447
%N A247164 Primes p such that Product_{d|(p-2)} phi(d) = Product_{d|(p-1)} phi(d) where phi(x) = Euler totient function (A000010).
%C A247164 Primes p such that A029940(p-2) = A029940(p-1).
%C A247164 First 5 known terms of Fermat primes (A019434) are terms of this sequence.
%F A247164 A029940(a(n)) = a(n) - 1.
%e A247164 Prime 17 is in the sequence because A029940(15) = A029940(16) = 64.
%o A247164 (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 A247164 Subsequence of A248796. Supersequence of A247203.
%Y A247164 Cf. A000010, A019434, A029940, A248795.
%K A247164 nonn,more
%O A247164 1,1
%A A247164 _Jaroslav Krizek_, Nov 21 2014
%E A247164 a(8)-a(9) from _Jinyuan Wang_, Jul 27 2025