a(n) = 68*2^n - 50 (n>=1).

Terms

a(0) =86a(1) =222a(2) =494a(3) =1038a(4) =2126a(5) =4302a(6) =8654a(7) =17358a(8) =34766a(9) =69582a(10) =139214a(11) =278478a(12) =557006a(13) =1114062a(14) =2228174a(15) =4456398a(16) =8912846a(17) =17825742a(18) =35651534a(19) =71303118a(20) =142606286a(21) =285212622a(22) =570425294a(23) =1140850638a(24) =2281701326a(25) =4563402702a(26) =9126805454a(27) =18253610958a(28) =36507221966a(29) =73014443982