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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 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.)