A104066 - OEIS

%I #20 Nov 08 2023 06:51:03

%S 11,23,71,263,1031,65543,262151,1048583,268435463,1073741831,

%T 274877906951,17592186044423,302231454903657293676551,

%U 309485009821345068724781063,316912650057057350374175801351

%N Primes of the form 2^k + 7.

%C Also primes of the form 4^n+7 (in this case, the associated n are in A217349). - _Bruno Berselli_, Oct 03 2012

%F a(n) = 2^A057195(n) + 7. - _Elmo R. Oliveira_, Nov 08 2023

%t a = Delete[Union[Flatten[Table[If [PrimeQ[2^n + 7] == True, 2^ n + 7, 0], {n, 1, 400}]]], 1]

%o (Magma) [a: n in [0..100 by 2] | IsPrime(a) where a is 2^n+7]; // _Vincenzo Librandi_, Jan 26 2011

%o (PARI) list(lim)=my(v=List(),t); for(n=1,logint(lim\1-7,4), if(ispseudoprime(t=4^n+7), listput(v,t))); Vec(v) \\ _Charles R Greathouse IV_, Nov 17 2017

%Y Cf. A000040, A057195 (numbers k such that 2^k + 7 is prime).

%K nonn

%O 1,1

%A _Roger L. Bagula_, Mar 02 2005