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

Terms

a(0) =0a(1) =0a(2) =0a(3) =2a(4) =2a(5) =2a(6) =4a(7) =8a(8) =12a(9) =18a(10) =30a(11) =50a(12) =80a(13) =128a(14) =208a(15) =338a(16) =546a(17) =882a(18) =1428a(19) =2312a(20) =3740a(21) =6050a(22) =9790a(23) =15842a(24) =25632a(25) =41472a(26) =67104a(27) =108578a(28) =175682a(29) =284258