a(n) = 63*2^(n+1) + 1.

Terms

a(0) =127a(1) =253a(2) =505a(3) =1009a(4) =2017a(5) =4033a(6) =8065a(7) =16129a(8) =32257a(9) =64513a(10) =129025a(11) =258049a(12) =516097a(13) =1032193a(14) =2064385a(15) =4128769a(16) =8257537a(17) =16515073a(18) =33030145a(19) =66060289a(20) =132120577a(21) =264241153a(22) =528482305a(23) =1056964609a(24) =2113929217a(25) =4227858433a(26) =8455716865a(27) =16911433729a(28) =33822867457