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

Terms

a(0) =2a(1) =1a(2) =4a(3) =12a(4) =72a(5) =480a(6) =4320a(7) =45360a(8) =564480a(9) =7983360a(10) =127008000a(11) =2235340800a(12) =43110144000a(13) =902918016000