E-trees with at most 2 colors.

Terms

a(0) =1a(1) =2a(2) =7a(3) =22a(4) =75a(5) =250a(6) =886a(7) =3150a(8) =11525a(9) =42698a(10) =160636a(11) =610694a(12) =2345584a(13) =9081850a(14) =35422281a(15) =139022744a(16) =548671671a(17) =2176051206a(18) =8668363781a(19) =34667284600a(20) =139140831224a(21) =560271494924