Catafusenes (see reference for precise definition).

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =12a(5) =94a(6) =612a(7) =3605a(8) =19992a(9) =106644a(10) =554184a(11) =2827902a(12) =14244120a(13) =71073860a(14) =352180920a(15) =1736103460a(16) =8525167680a(17) =41741310400a(18) =203929367040a(19) =994680578505