A247164 Primes p such that Product_{d|(p-2)} phi(d) = Product_{d|(p-1)} phi(d) where phi(x) = Euler totient function (A000010).

3, 5, 7, 17, 257, 65537, 991172807, 1872619667, 4081364447

Offset: 1

Author

Jaroslav Krizek, Nov 21 2014

Keywords

• nonn
• more

Comments

Primes p such that A029940(p-2) = A029940(p-1).

First 5 known terms of Fermat primes (A019434) are terms of this sequence.

Examples

			Prime 17 is in the sequence because A029940(15) = A029940(16) = 64.
		

Crossrefs

Subsequence of A248796. Supersequence of A247203.

Cf. A000010, A019434, A029940, A248795.

Programs

Magma

[n: n in [3..100000] |  IsPrime(n) and (&*[EulerPhi(d): d in Divisors(n-2)]) eq (&*[EulerPhi(d): d in Divisors(n-1)])];

Formula

A029940(a(n)) = a(n) - 1.

Extensions

a(8)-a(9) from Jinyuan Wang, Jul 27 2025