a(n) = a(n-1) + a(n-2) + a(n-4) with a(0) = 2, a(1) = 3, a(2) = 6, a(3) = 9.

Terms

a(0) =2a(1) =3a(2) =6a(3) =9a(4) =17a(5) =29a(6) =52a(7) =90a(8) =159a(9) =278a(10) =489a(11) =857a(12) =1505a(13) =2640a(14) =4634a(15) =8131a(16) =14270a(17) =25041a(18) =43945a(19) =77117a(20) =135332a(21) =237490a(22) =416767a(23) =731374a(24) =1283473a(25) =2252337a(26) =3952577a(27) =6936288a(28) =12172338a(29) =21360963