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A059242
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Numbers n such that 2^n + 5 is prime.
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18
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1, 3, 5, 11, 47, 53, 141, 143, 191, 273, 341, 16541, 34001, 34763, 42167, 193965, 282203
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OFFSET
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1,2
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COMMENTS
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The subsequence of primes starts 3, 5, 11, 47, 53, 191, ... - Vincenzo Librandi, Aug 07 2010
For k in this sequence, 2^(k-1)*(2^k+5) is in A141548: numbers of deficiency 6. - M. F. Hasler, Apr 23 2015
a(18) > 5*10^5. - Robert Price, Aug 23 2015
a(18) > 6*10^5. - Tyler NeSmith, Jan 18 2021
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LINKS
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Table of n, a(n) for n=1..17.
Keith Conrad, Square patterns and infinitude of primes, University of Connecticut, 2019.
Henri Lifchitz and Renaud Lifchitz (Editors), PRP Top Records, of the form 2^n+5.
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EXAMPLE
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2^3 + 5 = 13 is prime but 2^4 + 5 = 21 is not.
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MATHEMATICA
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Select[Range[20000], PrimeQ[2^#+5]&] (* Vladimir Joseph Stephan Orlovsky, Feb 26 2011 *)
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PROG
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(PARI) is(n)=ispseudoprime(2^n+5) \\ M. F. Hasler, Apr 23 2015
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CROSSREFS
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Sequence in context: A332968 A144467 A049883 * A175173 A268510 A004203
Adjacent sequences: A059239 A059240 A059241 * A059243 A059244 A059245
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KEYWORD
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nonn,hard,more
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AUTHOR
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Tony Davie (ad(AT)dcs.st-and.ac.uk), Jan 21 2001
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EXTENSIONS
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More terms from Santi Spadaro, Oct 04 2002
a(12) from Hans Havermann, Oct 07 2002
a(13)-a(15) from Charles R Greathouse IV, Oct 07 2011
a(16)-a(17) from Robert Price, Dec 06 2013
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STATUS
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approved
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