Number of unrooted achiral trees with n nodes.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =6a(6) =9a(7) =16a(8) =23a(9) =35a(10) =51a(11) =72a(12) =97a(13) =136a(14) =186a(15) =230a(16) =321a(17) =401a(18) =526a(19) =647a(20) =844a(21) =1000a(22) =1331a(23) =1539a(24) =1960a(25) =2299a(26) =2943a(27) =3307a(28) =4237a(29) =4779