G.f. satisfies: A(x) = 1 + x*A(x)^2/A(-x)^2.

Terms

a(0) =1a(1) =1a(2) =4a(3) =8a(4) =28a(5) =80a(6) =308a(7) =984a(8) =3980a(9) =13472a(10) =56164a(11) =197032a(12) =838396a(13) =3013872a(14) =13015188a(15) =47624568a(16) =207971436a(17) =771336512a(18) =3397886660a(19) =12736715592a(20) =56502898140a(21) =213618833808a(22) =953139545076