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%I #15 Feb 02 2024 09:01:41
%S 3,5,17,257,65537,83623937
%N Primes p such that phi(p-2) divides p-1 where phi is Euler's totient function (A000010).
%C The first 5 known Fermat primes from A019434 are terms.
%C Conjecture: also primes p such that 2*phi(p-2) = p-1 (i.e., primes in A232720).
%C a(7) > 10^25. - _Max Alekseyev_, Feb 02 2024
%o (Magma) [n: n in [3..10000000] | IsPrime(n) and (n-1) mod EulerPhi(n-2) eq 0]
%Y Subsequence of A249541.
%Y Cf. A000010, A019434, A050474, A203966, A232720.
%K nonn,more
%O 1,1
%A _Jaroslav Krizek_, Feb 25 2015
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