a(n) = 1 + Sum_{k=0..floor((n-1)/2)} a(k) * a(n-2*k-1).

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =11a(5) =21a(6) =40a(7) =78a(8) =151a(9) =294a(10) =572a(11) =1115a(12) =2172a(13) =4234a(14) =8252a(15) =16088a(16) =31361a(17) =61140a(18) =119191a(19) =232370a(20) =453010a(21) =883167a(22) =1721768a(23) =3356675a(24) =6543988a(25) =12757830a(26) =24871992a(27) =48489172a(28) =94531974a(29) =184294706