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A039698
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Numbers k such that phi(k) + 1 is prime.
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12
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1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 17, 18, 19, 21, 22, 23, 26, 27, 28, 29, 31, 32, 34, 36, 37, 38, 40, 41, 42, 43, 46, 47, 48, 49, 53, 54, 55, 57, 58, 59, 60, 61, 62, 63, 67, 71, 73, 74, 75, 76, 77, 79, 82, 83, 86, 88, 89, 91, 93, 94, 95, 97, 98, 99, 100, 101, 103
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OFFSET
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1,2
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COMMENTS
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For every prime p, the numbers p and 2p are terms of this sequence. - Vladimir Shevelev, May 10 2008
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LINKS
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EXAMPLE
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phi(10)+1 = 4+1 = 5, a prime number, so 10 is a term.
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MATHEMATICA
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PROG
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(Magma) [n: n in [1..200] | IsPrime(EulerPhi(n)+1)]; // Vincenzo Librandi, Aug 13 2013
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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