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

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =2a(8) =4a(9) =7a(10) =11a(11) =16a(12) =24a(13) =39a(14) =67a(15) =116a(16) =196a(17) =324a(18) =534a(19) =892a(20) =1516a(21) =2601a(22) =4463a(23) =7630a(24) =13022a(25) =22276a(26) =38286a(27) =66084a(28) =114328a(29) =197929