A254576 Primes p such that phi(p-2) divides p-1 where phi is Euler's totient function (A000010).

3, 5, 17, 257, 65537, 83623937

Offset: 1

Author

Jaroslav Krizek, Feb 25 2015

Keywords

• nonn
• more

Comments

The first 5 known Fermat primes from A019434 are terms.

Conjecture: also primes p such that 2*phi(p-2) = p-1 (i.e., primes in A232720).

a(7) > 10^25. - Max Alekseyev, Feb 02 2024

Crossrefs

Subsequence of A249541.

Cf. A000010, A019434, A050474, A203966, A232720.

Programs

Magma

[n: n in [3..10000000] | IsPrime(n) and (n-1) mod EulerPhi(n-2) eq 0];