E.g.f.: exp(1-sqrt(1-2*x-4*x^2)).

Terms

a(0) =1a(1) =1a(2) =6a(3) =31a(4) =301a(5) =3426a(6) =51751a(7) =926731a(8) =19691106a(9) =479961901a(10) =13256384851a(11) =408621822126