Revert transform of 1 - x - x^3.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =20a(5) =70a(6) =256a(7) =969a(8) =3762a(9) =14894a(10) =59904a(11) =244088a(12) =1005452a(13) =4180096a(14) =17516936a(15) =73913705a(16) =313774854a(17) =1339162028a(18) =5742691704a(19) =24731501410a(20) =106919054880a(21) =463844340060