a(n) = 15*2^(n+1) + 1.

Terms

a(0) =31a(1) =61a(2) =121a(3) =241a(4) =481a(5) =961a(6) =1921a(7) =3841a(8) =7681a(9) =15361a(10) =30721a(11) =61441a(12) =122881a(13) =245761a(14) =491521a(15) =983041a(16) =1966081a(17) =3932161a(18) =7864321a(19) =15728641a(20) =31457281a(21) =62914561a(22) =125829121a(23) =251658241a(24) =503316481a(25) =1006632961a(26) =2013265921a(27) =4026531841a(28) =8053063681a(29) =16106127361