Enumeration of fractal 321 avoiders.

Terms

a(0) =0a(1) =1a(2) =2a(3) =6a(4) =24a(5) =116a(6) =625a(7) =3580a(8) =21297a(9) =130084a(10) =810737a(11) =5135142a(12) =32961216a(13) =213940962a(14) =1401821021a(15) =9260154974a(16) =61603278951a(17) =412352572116