a(0) = a(1) = a(2) = 1; a(n) = a(n-3) + Sum_{k=0..n-4} a(k) * a(n-k-4).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =4a(7) =6a(8) =10a(9) =16a(10) =25a(11) =40a(12) =66a(13) =109a(14) =179a(15) =296a(16) =495a(17) =831a(18) =1396a(19) =2353a(20) =3985a(21) =6770a(22) =11523a(23) =19657a(24) =33621a(25) =57633a(26) =98969a(27) =170245a(28) =293371a(29) =506371