Largest safe prime less than 2^n.

Terms

a(0) =7a(1) =11a(2) =23a(3) =59a(4) =107a(5) =227a(6) =503a(7) =1019a(8) =2039a(9) =4079a(10) =8147a(11) =16223a(12) =32603a(13) =65267a(14) =130787a(15) =262127a(16) =524243a(17) =1048343a(18) =2097143a(19) =4194287a(20) =8388287a(21) =16776899a(22) =33553799a(23) =67108187a(24) =134217323a(25) =268435019a(26) =536870723a(27) =1073740439a(28) =2147483579a(29) =4294967087