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

Terms

a(0) =1a(1) =3a(2) =9a(3) =26a(4) =75a(5) =214a(6) =612a(7) =1747a(8) =4995a(9) =14294a(10) =40967a(11) =117560a(12) =337830a(13) =972027a(14) =2800210a(15) =8075889a(16) =23315775a(17) =67380458a(18) =194901273a(19) =564239262a(20) =1634763697a(21) =4739866803a(22) =13752309730a(23) =39926751310a(24) =115988095896a(25) =337138003197