a(n) is the least nonnegative integer k such that 2^n - k is a safe prime.

Terms

a(0) =1a(1) =5a(2) =9a(3) =5a(4) =21a(5) =29a(6) =9a(7) =5a(8) =9a(9) =17a(10) =45a(11) =161a(12) =165a(13) =269a(14) =285a(15) =17a(16) =45a(17) =233a(18) =9a(19) =17a(20) =321a(21) =317a(22) =633a(23) =677a(24) =405a(25) =437a(26) =189a(27) =1385a(28) =69a(29) =209