G.f.: 1/sqrt(1 - 6*x - 55*x^2).

Terms

a(0) =1a(1) =3a(2) =41a(3) =315a(4) =3345a(5) =31923a(6) =328889a(7) =3337323a(8) =34600225a(9) =359225955a(10) =3760299081a(11) =39497556123a(12) =416692693041