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

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =1a(5) =2a(6) =4a(7) =6a(8) =11a(9) =19a(10) =32a(11) =56a(12) =96a(13) =165a(14) =285a(15) =490a(16) =844a(17) =1454a(18) =2503a(19) =4311a(20) =7424a(21) =12784a(22) =22016a(23) =37913a(24) =65289a(25) =112434a(26) =193620a(27) =333430a(28) =574195a(29) =988811