E.g.f. 1/(1-x-x^4).

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =48a(5) =360a(6) =2880a(7) =25200a(8) =282240a(9) =3628800a(10) =50803200a(11) =758419200a(12) =12454041600a(13) =224172748800