E.g.f. (1-x)^2/(1-3x+x^3).

Terms

a(0) =1a(1) =1a(2) =8a(3) =66a(4) =768a(5) =11040a(6) =190800a(7) =3845520a(8) =88583040a(9) =2295578880a(10) =66098592000