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Search: id:A089920
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| A089920 |
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Prime exponents p such that 7^p - 2 is prime. |
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1
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OFFSET
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1,2
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COMMENT
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Except for p=2, 2, 5^p - 2 cannot be prime. This immediately follows from the fact that a number N = (3k+2)^p - 2 cannot be prime for p > 2 because N = 3H + 2^p - 2 = 3H + 2(2^(p-1)-1) is divisible by 3.
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PROGRAM
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(PARI) f(n) = for(x=1, n, if(ispseudoprime(7^prime(x)-2), print1(x, ", ")))
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CROSSREFS
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Sequence in context: A018242 A006248 A119571 this_sequence A118197 A092658 A113314
Adjacent sequences: A089917 A089918 A089919 this_sequence A089921 A089922 A089923
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KEYWORD
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nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Jan 11 2004
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