a(n) = 140*2^n - 127.

Terms

a(0) =13a(1) =153a(2) =433a(3) =993a(4) =2113a(5) =4353a(6) =8833a(7) =17793a(8) =35713a(9) =71553a(10) =143233a(11) =286593a(12) =573313a(13) =1146753a(14) =2293633a(15) =4587393a(16) =9174913a(17) =18349953a(18) =36700033a(19) =73400193a(20) =146800513a(21) =293601153a(22) =587202433a(23) =1174404993a(24) =2348810113a(25) =4697620353a(26) =9395240833a(27) =18790481793a(28) =37580963713a(29) =75161927553