Largest primitive factor of 2^(2n+1) + 1.

Terms

a(0) =3a(1) =1a(2) =11a(3) =43a(4) =19a(5) =683a(6) =2731a(7) =331a(8) =43691a(9) =174763a(10) =5419a(11) =2796203a(12) =4051a(13) =87211a(14) =3033169a(15) =715827883a(16) =20857a(17) =86171a(18) =25781083a(19) =22366891a(20) =8831418697a(22) =18837001a(23) =165768537521a(25) =6529a(27) =48912491a(28) =160465489