E.g.f.: 1 / ((1 + x) * sqrt(1 - 2*x)).

Terms

a(0) =1a(1) =0a(2) =3a(3) =6a(4) =81a(5) =540a(6) =7155a(7) =85050a(8) =1346625a(9) =22339800a(10) =431331075a(11) =9004668750a(12) =208178118225