a(0) = a(1) = a(2) = 1; a(n) = Sum_{k=1..n-3} a(k) * a(n-k-3).

Terms

a(0) =1a(1) =1a(2) =1a(3) =0a(4) =1a(5) =2a(6) =2a(7) =2a(8) =4a(9) =8a(10) =10a(11) =13a(12) =24a(13) =42a(14) =61a(15) =90a(16) =156a(17) =265a(18) =410a(19) =646a(20) =1093a(21) =1834a(22) =2948a(23) =4789a(24) =8050a(25) =13475a(26) =22129a(27) =36570a(28) =61435a(29) =103039