a(n) = a(n-1) + a(n-3), with a(0) = 1, a(1) = 4, a(2) = 8.

Terms

a(0) =1a(1) =4a(2) =8a(3) =9a(4) =13a(5) =21a(6) =30a(7) =43a(8) =64a(9) =94a(10) =137a(11) =201a(12) =295a(13) =432a(14) =633a(15) =928a(16) =1360a(17) =1993a(18) =2921a(19) =4281a(20) =6274a(21) =9195a(22) =13476a(23) =19750a(24) =28945a(25) =42421a(26) =62171a(27) =91116a(28) =133537a(29) =195708