a(n) = 11*2^n + 1.

Terms

a(0) =12a(1) =23a(2) =45a(3) =89a(4) =177a(5) =353a(6) =705a(7) =1409a(8) =2817a(9) =5633a(10) =11265a(11) =22529a(12) =45057a(13) =90113a(14) =180225a(15) =360449a(16) =720897a(17) =1441793a(18) =2883585a(19) =5767169a(20) =11534337a(21) =23068673a(22) =46137345a(23) =92274689a(24) =184549377a(25) =369098753a(26) =738197505a(27) =1476395009a(28) =2952790017a(29) =5905580033