a(n)= 3*a(n-1) +a(n-2) -3*a(n-3) +a(n-4)+ 2*a(n-5) -a(n-6) -a(n-7).

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =3a(5) =5a(6) =8a(7) =23a(8) =67a(9) =208a(10) =635a(11) =1943a(12) =5940a(13) =18169a(14) =55579a(15) =170024a(16) =520127a(17) =1591139a(18) =4867506a(19) =14890349a(20) =45551563a(21) =139348310a(22) =426285079a(23) =1304062953a(24) =3989302624a(25) =12203809169a(26) =37333081059a(27) =114206877712a(28) =349374081829