Number of 2-trees rooted at an asymmetric end-edge.

Terms

a(0) =0a(1) =1a(2) =3a(3) =13a(4) =52a(5) =229a(6) =1024a(7) =4749a(8) =22454a(9) =108299a(10) =529896a(11) =2625903a(12) =13148268a(13) =66428383a(14) =338197609a(15) =1733399552a(16) =8936746984a(17) =46315049443a(18) =241146306914