The number of ordered trees with bicolored single edges on the boundary.

Terms

a(0) =1a(1) =2a(2) =5a(3) =15a(4) =50a(5) =175a(6) =625a(7) =2251a(8) =8142a(9) =29544a(10) =107538a(11) =392726a(12) =1439204a(13) =5292833a(14) =19533241a(15) =72333107a(16) =268728214a(17) =1001448308a(18) =3742866166a(19) =14026901282a(20) =52701685564a(21) =198481560878a(22) =749170991770