a(n) = Sum_{i=1..floor((n+1)/4)} a(2*i-1) * a(n-2*i+1), with a(1)=a(2)=1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =2a(7) =3a(8) =4a(9) =6a(10) =10a(11) =16a(12) =25a(13) =39a(14) =67a(15) =110a(16) =177a(17) =289a(18) =494a(19) =828a(20) =1369a(21) =2274a(22) =3927a(23) =6662a(24) =11172a(25) =18834a(26) =32657a(27) =55915a(28) =94911a(29) =161435