A247164 - OEIS

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

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OFFSET

1,1

COMMENTS

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

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

Subsequence of A248796. Supersequence of A247203.

LINKS

FORMULA

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

EXAMPLE

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

PROG

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

CROSSREFS

KEYWORD

nonn,more

AUTHOR

STATUS

approved