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A110931
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Numbers k such that 2*k^k - 1 is prime.
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7
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OFFSET
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1,1
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COMMENTS
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a(5) > 4000. - Ray G. Opao, Oct 23 2014
a(5) > 101000. - Serge Batalov, Apr 13 2018
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LINKS
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Table of n, a(n) for n=1..4.
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EXAMPLE
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3 is in the sequence since 2*3^3 - 1 = 53 is prime.
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MATHEMATICA
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Select[Range[1000], PrimeQ[2*#^# - 1] &] (* Vaclav Kotesovec, Oct 31 2014 *)
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PROG
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(PARI) for(n=1, 2000, 1; if(isprime(2*n^n-1), print(n))) \\ Ray G. Opao, Oct 23 2014
(MAGMA) [n: n in [0..500] | IsPrime(2*n^n-1)]; // Vincenzo Librandi, Nov 01 2014
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CROSSREFS
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Numbers k such that b*k^k - b + 1 is prime: this sequence (b=2), A301521 (b=4), A302123 (b=6).
Cf. A110932, A062207, A108318.
Sequence in context: A177505 A068104 A065586 * A097654 A156986 A066849
Adjacent sequences: A110928 A110929 A110930 * A110932 A110933 A110934
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KEYWORD
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more,nonn,hard
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AUTHOR
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Ray G. Opao, Sep 25 2005
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STATUS
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approved
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