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

Terms

a(0) =1a(1) =1a(2) =1a(3) =-1a(4) =-3a(5) =-1a(6) =5a(7) =23a(8) =29a(9) =-33a(10) =-139a(11) =-217a(12) =13a(13) =943a(14) =1765a(15) =-1545a(16) =-8963a(17) =-11265a(18) =6229a(19) =73671a(20) =126701a(21) =-65713a(22) =-567611a(23) =-793449a(24) =415197a(25) =4231583a(26) =7471669a(27) =-4933529a(28) =-37928499a(29) =-52823313