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

Terms

a(0) =1a(1) =0a(2) =1a(3) =0a(4) =1a(5) =1a(6) =2a(7) =2a(8) =3a(9) =4a(10) =6a(11) =9a(12) =12a(13) =18a(14) =24a(15) =36a(16) =49a(17) =72a(18) =99a(19) =144a(20) =200a(21) =289a(22) =404a(23) =581a(24) =816a(25) =1168a(26) =1646a(27) =2350a(28) =3320a(29) =4730