a(n) = s(2*n) where s(0) = 0, s(1) = s(2) = 1, s(n) = abs(Sum_{k=2..n-1} (-1)^k * s(n-k) * s(k)).

Terms

a(0) =0a(1) =1a(2) =0a(3) =1a(4) =1a(5) =1a(6) =0a(7) =1a(8) =2a(9) =1a(10) =2a(11) =3a(12) =1a(13) =3a(14) =4a(15) =1a(16) =3a(17) =5a(18) =6a(19) =1a(20) =7a(21) =29a(22) =14a(23) =41a(24) =82a(25) =39a(26) =58a(27) =109a(28) =119a(29) =1