Expansion of e.g.f. 1/(1-x-x^3).

Terms

a(0) =1a(1) =1a(2) =2a(3) =12a(4) =72a(5) =480a(6) =4320a(7) =45360a(8) =524160a(9) =6894720a(10) =101606400a(11) =1636588800a(12) =28740096000a(13) =547977830400