Number of rooted trees with n nodes, 2 of which are labeled.

Terms

a(0) =2a(1) =9a(2) =34a(3) =119a(4) =401a(5) =1316a(6) =4247a(7) =13532a(8) =42712a(9) =133816a(10) =416770a(11) =1291731a(12) =3987444a(13) =12266845a(14) =37627230a(15) =115125955a(16) =351467506a(17) =1070908135a(18) =3257389088a(19) =9892759091a(20) =30002923380a(21) =90879555521a(22) =274963755791a(23) =831064788976