What are max. number of binary trees formed using three unlabeled nodes?

[anshika-sharma-ac2988d4 (Anshika Sharma)]

What are max. number of binary trees formed using three unlabeled nodes ?

[sakshi-srivastava-f3c2a4a4 (Sakshi Srivastava)]

This is expression is equal to the result of the Catalan Number, Cn = (2n)!/(n+1)!*n!

So the answer will be: 5