Number of trees with n 2-colored nodes.

Terms

a(0) =2a(1) =3a(2) =6a(3) =18a(4) =54a(5) =189a(6) =700a(7) =2778a(8) =11486a(9) =49377a(10) =217936a(11) =984818a(12) =4533004a(13) =21198962a(14) =100471862a(15) =481754806a(16) =2333465628a(17) =11404047817a(18) =56177574628a(19) =278710061814