a(n) = 4*a(n-1) + 7*a(n-2).

Terms

a(0) =0a(1) =1a(2) =4a(3) =23a(4) =120a(5) =641a(6) =3404a(7) =18103a(8) =96240a(9) =511681a(10) =2720404a(11) =14463383a(12) =76896360a(13) =408829121a(14) =2173591004a(15) =11556167863a(16) =61439808480a(17) =326652408961