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A281624
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Numbers n such that 2^phi(n) + 1 is prime (Fermat prime).
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0
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1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 16, 17, 20, 24, 30, 32, 34, 40, 48, 60
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OFFSET
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1,2
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COMMENTS
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If there are only 5 Fermat primes, sequence is finite with 20 terms; corresponding values of Fermat primes: 3, 3, 5, 5, 17, 5, 17, 17, 17, 257, 257, 65537, 257, 257, 257, 65537, 65537, 65537, 65537, 65537.
Number of numbers k such that 2^phi(k) + 1 = A019434(n) for n = 1-5: 2, 3, 4, 5, 6.
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LINKS
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EXAMPLE
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10 is a term because 2^phi(10) + 1 = 2^4 + 1 = 17 (prime).
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PROG
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(Magma) [n: n in[1..10000] | IsPrime(2^(EulerPhi(n)) + 1)]
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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