a(0) = 6; for n>0, a(n) = 2*a(n-1) - 1.

Terms

a(0) =6a(1) =11a(2) =21a(3) =41a(4) =81a(5) =161a(6) =321a(7) =641a(8) =1281a(9) =2561a(10) =5121a(11) =10241a(12) =20481a(13) =40961a(14) =81921a(15) =163841a(16) =327681a(17) =655361a(18) =1310721a(19) =2621441a(20) =5242881a(21) =10485761a(22) =20971521a(23) =41943041a(24) =83886081a(25) =167772161a(26) =335544321a(27) =671088641a(28) =1342177281a(29) =2684354561