a(n) = 69*2^n - 42 (n>=1).

Terms

a(0) =96a(1) =234a(2) =510a(3) =1062a(4) =2166a(5) =4374a(6) =8790a(7) =17622a(8) =35286a(9) =70614a(10) =141270a(11) =282582a(12) =565206a(13) =1130454a(14) =2260950a(15) =4521942a(16) =9043926a(17) =18087894a(18) =36175830a(19) =72351702a(20) =144703446a(21) =289406934a(22) =578813910a(23) =1157627862a(24) =2315255766a(25) =4630511574a(26) =9261023190a(27) =18522046422a(28) =37044092886a(29) =74088185814