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

Terms

a(0) =2a(1) =1a(2) =2a(3) =12a(4) =24a(5) =120a(6) =1440a(7) =5040a(8) =40320a(9) =725760a(10) =3628800a(11) =39916800a(12) =958003200a(13) =6227020800a(14) =87178291200