Generalized Catalan numbers 2*x*A(x)^2 -A(x) +1 -x =0.

Terms

a(0) =1a(1) =1a(2) =4a(3) =18a(4) =88a(5) =456a(6) =2464a(7) =13736a(8) =78432a(9) =456416a(10) =2697088a(11) =16141120a(12) =97632000a(13) =595912960a(14) =3665728512a(15) =22703097472a(16) =141448381952a(17) =885934151168