How many different binary trees are possible with n nodes?

Problem statement: what do you say, how many different binary trees are possible with n nodes?

• In general, 

1. if there are n nodes,
2. then there exist 2ⁿ - n different trees

• example - 

1. number of node = 3
2. then different trees = 2³ - 3 = 8 - 3 = 5