Prime powers p^k with even exponents k > 0 such that (1 + p^k)/2 is prime.

Terms

a(0) =9a(1) =25a(2) =81a(3) =121a(4) =361a(5) =625a(6) =841a(7) =2401a(8) =3481a(9) =3721a(10) =5041a(11) =6241a(12) =10201a(13) =14641a(14) =17161a(15) =19321a(16) =28561a(17) =32761a(18) =39601a(19) =73441a(20) =83521a(21) =121801a(22) =143641a(23) =167281a(24) =201601a(25) =212521a(26) =271441a(27) =279841a(28) =323761a(29) =326041