E,g.f.: exp(1-sqrt(1-2*x-3*x^2)).

Terms

a(0) =1a(1) =1a(2) =5a(3) =25a(4) =217a(5) =2321a(6) =32221a(7) =536425a(8) =10547825a(9) =238451617a(10) =6103391221a(11) =174418724921