n*(n-1)*4^n.

Terms

a(0) =0a(1) =0a(2) =32a(3) =384a(4) =3072a(5) =20480a(6) =122880a(7) =688128a(8) =3670016a(9) =18874368a(10) =94371840a(11) =461373440a(12) =2214592512a(13) =10468982784a(14) =48855252992a(15) =225485783040