a(n) = 2*a(n-1) - a(n-2) + a(n-4), n>3, a(0)=0, a(1)=a(2)=1, a(3)=3.

Terms

a(0) =0a(1) =1a(2) =1a(3) =3a(4) =5a(5) =8a(6) =12a(7) =19a(8) =31a(9) =51a(10) =83a(11) =134a(12) =216a(13) =349a(14) =565a(15) =915a(16) =1481a(17) =2396a(18) =3876a(19) =6271a(20) =10147a(21) =16419a(22) =26567a(23) =42986a(24) =69552a(25) =112537a(26) =182089a(27) =294627a(28) =476717a(29) =771344