a = Delete[Union[Flatten[Table[If [PrimeQ[2^n + 7] == True, 2^ n + 7, 0], {n, 1, 400}]]], 1]
PROG
(Magma) [a: n in [0..100 by 2] | IsPrime(a) where a is 2^n+7]; // Vincenzo Librandi, Jan 26 2011
(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
CROSSREFS
Cf. A000040, A057195 (numbers k such that 2^k + 7 is prime).
