a(n) is the smallest number m such that 2im+1 is composite for all i, 0<i<n+1.

Terms

a(0) =4a(1) =12a(2) =19a(3) =19a(4) =59a(5) =92a(6) =159a(7) =159a(8) =159a(9) =227a(10) =227a(11) =256a(12) =256a(13) =256a(14) =514a(15) =514a(16) =706a(17) =706a(18) =706a(19) =706a(20) =706a(21) =706a(22) =706a(23) =1466a(24) =1466a(25) =1466a(26) =1466a(27) =1466a(28) =1466a(29) =5207