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A075469
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Maximal m such that n^n-m and n^n+m are both primes, or -1 if there is no such m.
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2
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1, 20, 253, 3122, 46651, 823540, 16777155, 387420478, 9999999939, 285311670528, 8916100448227, 302875106592216, 11112006825558003, 437893890380859368, 18446744073709551537, 827240261886336764070, 39346408075296537575383
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OFFSET
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2,2
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COMMENTS
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Are there any negative terms?
Of course the Goldbach conjecture implies that the answer is "no"; further, the first thousand terms are positive. - Charles R Greathouse IV, Mar 16 2016
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LINKS
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FORMULA
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EXAMPLE
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a(4) = 253 since 4^4-253 = 3 and 4^4+253 = 509 are both prime.
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PROG
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(PARI) a(n)=my(N=n^n); forprime(p=2, N, if(isprime(2*N-p), return(N-p))); -1 \\ Charles R Greathouse IV, Mar 16 2016
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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