Number of rooted trees with n generators.

Terms

a(0) =1a(1) =2a(2) =5a(3) =16a(4) =53a(5) =194a(6) =730a(7) =2868a(8) =11526a(9) =47370a(10) =197786a(11) =837467a(12) =3585696a(13) =15501423a(14) =67563442a(15) =296579626a(16) =1309973823a(17) =5817855174a(18) =25964218471a(19) =116379947718a(20) =523699384013