a(n) = 4*a(n-1) + (n-6)*a(n-2).

Terms

a(0) =0a(1) =1a(2) =4a(3) =14a(4) =52a(5) =208a(6) =884a(7) =3952a(8) =18460a(9) =89648a(10) =450892a(11) =2341456a(12) =12522068a(13) =68819920a(14) =387978292a(15) =2240112368a(16) =13228210684a(17) =79794191152a(18) =491143503500