Number of black-rooted red-black trees with n internal nodes.

Terms

a(0) =1a(1) =2a(2) =2a(3) =4a(4) =8a(5) =16a(6) =33a(7) =56a(8) =90a(9) =164a(10) =330a(11) =688a(12) =1440a(13) =3008a(14) =6291a(15) =13168a(16) =27604a(17) =57896a(18) =120730a(19) =248312a(20) =501464a(21) =995664a(22) =1954582a(23) =3821328a(24) =7495996a(25) =14848472a(26) =29815976a(27) =60741680a(28) =125363472a(29) =261452256