a(n) = (2n+1)*8^n.

Terms

a(0) =1a(1) =24a(2) =320a(3) =3584a(4) =36864a(5) =360448a(6) =3407872a(7) =31457280a(8) =285212672a(9) =2550136832a(10) =22548578304a(11) =197568495616