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A110931
Numbers k such that 2*k^k - 1 is prime.
7
2, 3, 357, 1400, 205731, 296598
OFFSET
1,1
COMMENTS
a(5) > 4000. - Ray G. Opao, Oct 23 2014
a(5) > 101000. - Serge Batalov, Apr 13 2018
EXAMPLE
3 is in the sequence since 2*3^3 - 1 = 53 is prime.
MATHEMATICA
Select[Range[1000], PrimeQ[2*#^# - 1] &] (* Vaclav Kotesovec, Oct 31 2014 *)
PROG
(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
CROSSREFS
Numbers k such that b*k^k - b + 1 is prime: this sequence (b=2), A301521 (b=4), A302123 (b=6).
Sequence in context: A068104 A065586 A375236 * A355323 A097654 A156986
KEYWORD
more,nonn,hard
AUTHOR
Ray G. Opao, Sep 25 2005
EXTENSIONS
a(5-6) from Ryan Propper, Jul 24-28 2022
STATUS
approved