a(n) = Hypergeometric([-n, n], [1], 2).

Terms

a(0) =1a(1) =-1a(2) =5a(3) =-25a(4) =129a(5) =-681a(6) =3653a(7) =-19825a(8) =108545a(9) =-598417a(10) =3317445a(11) =-18474633a(12) =103274625a(13) =-579168825a(14) =3256957317a(15) =-18359266785a(16) =103706427393a(17) =-586889743905