a(n) = 16*3^n - 48.

Terms

a(0) =0a(1) =96a(2) =384a(3) =1248a(4) =3840a(5) =11616a(6) =34944a(7) =104928a(8) =314880a(9) =944736a(10) =2834304a(11) =8503008a(12) =25509120a(13) =76527456a(14) =229582464a(15) =688747488a(16) =2066242560a(17) =6198727776a(18) =18596183424a(19) =55788550368a(20) =167365651200a(21) =502096953696