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A254576 Primes p such that phi(p-2) divides p-1 where phi is Euler's totient function (A000010). 2
3, 5, 17, 257, 65537, 83623937 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The first 5 known Fermat primes from A019434 are terms.

Subsequence of A249541.

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

If a(7) exists, it must be bigger than 4*10^9.

LINKS

Table of n, a(n) for n=1..6.

PROG

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

CROSSREFS

Cf. A000010, A019434, A249541.

Sequence in context: A050922 A260476 A070592 * A232720 A272061 A247203

Adjacent sequences:  A254573 A254574 A254575 * A254577 A254578 A254579

KEYWORD

nonn,more

AUTHOR

Jaroslav Krizek, Feb 25 2015

STATUS

approved

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Last modified December 9 13:50 EST 2019. Contains 329877 sequences. (Running on oeis4.)