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

Terms

a(0) =5a(1) =6a(2) =7a(3) =9a(4) =11a(5) =13a(6) =14a(7) =21a(8) =23a(9) =41a(10) =46a(11) =89a(12) =110a(13) =389a(14) =413a(15) =489a(16) =869a(17) =1589a(18) =1713a(19) =2831a(20) =10843a(21) =11257a(22) =16949a(23) =24513a(24) =39621a(25) =43349a(26) =62941a(27) =96094a(28) =139237a(29) =145289