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%I #30 Feb 02 2024 09:05:48
%S 3,4,5,17,257,65537,83623937,4294967297,6992962672132097
%N Numbers m such that phi(m-2) divides m-1 where phi is Euler's totient function (A000010).
%C The first 5 known Fermat primes from A019434 are in this sequence.
%C Corresponding values of numbers k(m) = (m-1) / phi(m-2): 2, 3, 2, 2, 2, 2, 2, 2, ...
%C Conjecture: 4 is the only number m such that 3*phi(m-2) = m-1. (See comment in A203966.)
%F a(n) = A203966(n+1) + 2. - _Max Alekseyev_, Feb 01 2024
%e 4 is in the sequence because phi(4-2) = 1 divides 4-1 = 3.
%o (Magma) [n: n in [3..10000000] | (n-1) mod EulerPhi(n-2) eq 0]
%Y Supersequence of A232720 and A254576.
%Y Cf. A000010, A019434, A203966, A232720, A254576.
%K nonn,more
%O 1,1
%A _Jaroslav Krizek_, Feb 25 2015
%E a(9) confirmed by _Max Alekseyev_, Feb 01 2024
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