Number of palindromic plane trees with n nodes.

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =6a(5) =10a(6) =20a(7) =35a(8) =68a(9) =122a(10) =234a(11) =426a(12) =808a(13) =1484a(14) =2798a(15) =5167a(16) =9700a(17) =17974a(18) =33656a(19) =62498a(20) =116826a(21) =217236a(22) =405646a(23) =754938a(24) =1408736a(25) =2623188a(26) =4892848a(27) =9114036a(28) =16995110a(29) =31664136