Number of two element anti-chains in Riordan trees on n edges (also called non-redundant trees, i.e., ordered trees where no vertex has out-degree equal to 1).

A139263

Number of two element anti-chains in Riordan trees on n edges (also called non-redundant trees, i.e., ordered trees where no vertex has out-degree equal to 1).

Terms

    a(0) =0a(1) =0a(2) =1a(3) =3a(4) =14a(5) =48a(6) =172a(7) =580a(8) =1941a(9) =6373a(10) =20725a(11) =66763a(12) =213575a(13) =679141a(14) =2148948a(15) =6771068a(16) =21257741a(17) =66529077a(18) =207639925a(19) =646480555a(20) =2008458669a(21) =6227766899a(22) =19277394308a(23) =59577651108a(24) =183865477474a(25) =566700165898

External references