generate-trees-of-order

(generate-trees-of-order n) returns a list of all unique trees of order $n$. For instance:

CL-USER 2 > (generate-trees-of-order 4)
(#S(Graph :Adjacency-Matrix ((Nil T Nil Nil) (T Nil T T) 
(Nil T Nil Nil) (Nil T Nil Nil)) :Internal-Order Nil 
:Internal-G6-String "Ci" :Internal-Canonical-Label "CF" 
:Internal-Dreadnaut-String Nil :Internal-Graceful-Labeling 
Nil) #S(Graph :Adjacency-Matrix ((Nil T Nil Nil) (T Nil T Nil) 
(Nil T Nil T) (Nil Nil T Nil)) :Internal-Order Nil 
:Internal-G6-String "Ch" :Internal-Canonical-Label "CR" 
:Internal-Dreadnaut-String Nil :Internal-Graceful-Labeling Nil))

CL-USER 3 > (length (generate-trees-of-order 4))
2

CL-USER 4 > (generate-trees-of-order 7)
(#S(Graph :Adjacency-Matrix ((Nil T Nil Nil Nil Nil Nil) 
(T Nil T T T T T) (Nil T Nil Nil Nil Nil Nil) 
(Nil T Nil Nil Nil Nil Nil) (Nil T Nil Nil Nil Nil Nil) 

...

:Internal-Canonical-Label "F@IQO" 
:Internal-Dreadnaut-String Nil :Internal-Graceful-Labeling Nil))

CL-USER 5 > (length (generate-trees-of-order 7))
11