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

Terms

a(0) =1a(1) =1a(2) =5a(3) =21a(4) =105a(5) =553a(6) =3053a(7) =17405a(8) =101713a(9) =606033a(10) =3667797a(11) =22485477a(12) =139340985a(13) =871429497a(14) =5492959293a(15) =34862161869a(16) =222592918689