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

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =5a(5) =8a(6) =20a(7) =38a(8) =83a(9) =173a(10) =362a(11) =767a(12) =1604a(13) =3386a(14) =7112a(15) =14969a(16) =31493a(17) =66242a(18) =139385a(19) =293204a(20) =616880a(21) =1297766a(22) =2730251a(23) =5743937a(24) =12084050a(25) =25422563a(26) =53483960a(27) =112519838a(28) =236719568a(29) =498011393