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A249541
Numbers m such that phi(m-2) divides m-1 where phi is Euler's totient function (A000010).
2
3, 4, 5, 17, 257, 65537, 83623937, 4294967297, 6992962672132097
OFFSET
1,1
COMMENTS
The first 5 known Fermat primes from A019434 are in this sequence.
Corresponding values of numbers k(m) = (m-1) / phi(m-2): 2, 3, 2, 2, 2, 2, 2, 2, ...
Conjecture: 4 is the only number m such that 3*phi(m-2) = m-1. (See comment in A203966.)
FORMULA
a(n) = A203966(n+1) + 2. - Max Alekseyev, Feb 01 2024
EXAMPLE
4 is in the sequence because phi(4-2) = 1 divides 4-1 = 3.
PROG
(Magma) [n: n in [3..10000000] | (n-1) mod EulerPhi(n-2) eq 0]
CROSSREFS
Supersequence of A232720 and A254576.
Sequence in context: A174326 A224890 A263810 * A059184 A161961 A161474
KEYWORD
nonn,more
AUTHOR
Jaroslav Krizek, Feb 25 2015
EXTENSIONS
a(9) confirmed by Max Alekseyev, Feb 01 2024
STATUS
approved