2^(n-3)n(9n^2-9n+4).

Terms

a(0) =0a(1) =1a(2) =22a(3) =174a(4) =896a(5) =3680a(6) =13152a(7) =42784a(8) =130048a(9) =375552a(10) =1041920a(11) =2799104a(12) =7323648a(13) =18743296a(14) =47079424a(15) =116367360a(16) =283639808a(17) =682950656a(18) =1626734592a(19) =3837657088a(20) =8975810560a(21) =20831010816a(22) =48005906432a(23) =109926416384a(24) =250248953856