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A191620
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Least k such that (2^n-k)*2^n - 1 is a prime number
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14
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0, 1, 2, 1, 1, 2, 2, 7, 1, 1, 14, 2, 11, 11, 2, 22, 7, 1, 2, 8, 2, 11, 14, 32, 2, 13, 2, 11, 52, 8, 10, 49, 13, 11, 4, 11, 31, 1, 23, 64, 11, 47, 20, 38, 1, 14, 4, 88, 7, 1, 47, 14, 22, 8, 2, 14, 1, 31, 20, 71, 20, 4, 44, 101, 38, 43, 80, 49, 11, 59, 4, 8
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OFFSET
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1,3
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COMMENTS
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Does a(n) exist for every n? This does not seem to be known, even on the GRH; see Heath-Brown. [Charles R Greathouse IV, Dec 27 2011]
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LINKS
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MATHEMATICA
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Table[a = 0; While[! PrimeQ[(2^n - a)*2^n - 1], a++]; a, {n, 100}] (* T. D. Noe, Jun 11 2011 *)
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PROG
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(PARI) a(n)=forstep(k=4^n-1, 1, -2^n, if(ispseudoprime(k), return(2^n-(k+1)>>n))) \\ Charles R Greathouse IV, Dec 27 2011
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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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