a(n)= 8*a(n-1) -16*a(n-2) +4*a(n-4).

Terms

a(0) =0a(1) =4a(2) =18a(3) =76a(4) =320a(5) =1360a(6) =5832a(7) =25200a(8) =109568a(9) =478784a(10) =2100512a(11) =9244352a(12) =40784896a(13) =180284672a(14) =798121088a(15) =3537391360a(16) =15692333056a(17) =69661541376a(18) =309407486464