a(n) = 2^(n-1)*ChebyshevU(n-1, 2).

Terms

a(0) =0a(1) =1a(2) =8a(3) =60a(4) =448a(5) =3344a(6) =24960a(7) =186304a(8) =1390592a(9) =10379520a(10) =77473792a(11) =578272256a(12) =4316282880a(13) =32217174016a(14) =240472260608