a(n) = 4^n * (2^n - 1).

Terms

a(0) =0a(1) =4a(2) =48a(3) =448a(4) =3840a(5) =31744a(6) =258048a(7) =2080768a(8) =16711680a(9) =133955584a(10) =1072693248a(11) =8585740288a(12) =68702699520a(13) =549688705024