a(n) = (n-4)*(n-3)*2^(n-2).

Terms

a(0) =3a(1) =3a(2) =2a(3) =0a(4) =0a(5) =16a(6) =96a(7) =384a(8) =1280a(9) =3840a(10) =10752a(11) =28672a(12) =73728a(13) =184320a(14) =450560a(15) =1081344a(16) =2555904a(17) =5963776a(18) =13762560a(19) =31457280a(20) =71303168a(21) =160432128a(22) =358612992a(23) =796917760a(24) =1761607680a(25) =3875536896a(26) =8489271296a(27) =18522046464a(28) =40265318400a(29) =87241523200