

A059242


Numbers n such that 2^n + 5 is prime.


18



1, 3, 5, 11, 47, 53, 141, 143, 191, 273, 341, 16541, 34001, 34763, 42167, 193965, 282203
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OFFSET

1,2


COMMENTS

The subsequence of primes starts 3, 5, 11, 47, 53, 191, ...  Vincenzo Librandi, Aug 07 2010
For k in this sequence, 2^(k1)*(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


LINKS

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.


EXAMPLE

2^3 + 5 = 13 is prime but 2^4 + 5 = 21 is not.


MATHEMATICA

Select[Range[20000], PrimeQ[2^#+5]&] (* Vladimir Joseph Stephan Orlovsky, Feb 26 2011 *)


PROG

(PARI) is(n)=ispseudoprime(2^n+5) \\ M. F. Hasler, Apr 23 2015


CROSSREFS

Sequence in context: A332968 A144467 A049883 * A175173 A268510 A004203
Adjacent sequences: A059239 A059240 A059241 * A059243 A059244 A059245


KEYWORD

nonn,hard,more


AUTHOR

Tony Davie (ad(AT)dcs.stand.ac.uk), Jan 21 2001


EXTENSIONS

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


STATUS

approved



