Number of identity matched trees with n nodes.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =4a(5) =16a(6) =64a(7) =252a(8) =1018a(9) =4182a(10) =17510a(11) =74510a(12) =322034a(13) =1410362a(14) =6251114a(15) =27998532a(16) =126583634a(17) =577079333a(18) =2650573354a(19) =12256481666a(20) =57021299394a(21) =266754944481