a(n) = 2^(n-1)*(3*n-4).

Terms

a(0) =-2a(1) =-1a(2) =4a(3) =20a(4) =64a(5) =176a(6) =448a(7) =1088a(8) =2560a(9) =5888a(10) =13312a(11) =29696a(12) =65536a(13) =143360a(14) =311296a(15) =671744a(16) =1441792a(17) =3080192a(18) =6553600a(19) =13893632a(20) =29360128a(21) =61865984a(22) =130023424a(23) =272629760a(24) =570425344a(25) =1191182336a(26) =2483027968a(27) =5167382528a(28) =10737418240