Number of identity trees with 2-colored nodes.

Terms

a(0) =1a(1) =2a(2) =1a(3) =2a(4) =6a(5) =20a(6) =69a(7) =270a(8) =1026a(9) =4120a(10) =16794a(11) =70230a(12) =298306a(13) =1288912a(14) =5642559a(15) =25007756a(16) =111998920a(17) =506348902a(18) =2308338456a(19) =10602357346a(20) =49026021552a(21) =228085486580