human
Write a function which returns nth catalan number. Here is a solution in Python:
What is a the Python program you requested?
assistant
#Here is the Python program you requested.
 def catalan_number(num):
    if num <=1:
         return 1   
    res_num = 0
    for i in range(num):
        res_num += catalan_number(i) * catalan_number(num-i-1)
    return res_num