Primes of the form Phi(k, -2), where Phi is the cyclotomic polynomial.

Terms

a(0) =3a(1) =5a(2) =11a(3) =7a(4) =43a(5) =17a(6) =31a(7) =683a(8) =13a(9) =2731a(10) =127a(11) =331a(12) =257a(13) =43691a(14) =73a(15) =174763a(16) =5419a(17) =2796203a(18) =241a(19) =8191a(20) =151a(21) =715827883a(22) =65537a(23) =131071a(24) =524287a(25) =22366891a(26) =61681a(28) =18837001a(30) =262657a(31) =15790321