Numbers k such that 2^k + 21 is prime.

Terms

a(0) =1a(1) =3a(2) =4a(3) =5a(4) =7a(5) =8a(6) =11a(7) =15a(8) =16a(9) =19a(10) =44a(11) =48a(12) =51a(13) =52a(14) =61a(15) =163a(16) =196a(17) =456a(18) =492a(19) =911a(20) =997a(21) =1616a(22) =1631a(23) =1647a(24) =1803a(25) =1899a(26) =3112a(27) =3584a(28) =3956a(29) =6848