Question: 
Write a function for nth catalan number.


Model's Code:
def catalan_number(n):
    if n == 0:
        return 1
    C = [0] * (n + 1)
    C[0] = 1
    for i in range(1, n + 1):
        C[i] = 0
        for j in range(i):
            C[i] += C[j] * C[i - 1 - j]
    return C[n]



Sample Correct Code:
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


Asserts:
assert catalan_number(10)==16796
assert catalan_number(9)==4862
assert catalan_number(7)==429


Tests:
Test 1 of 3: PASS
Test 2 of 3: PASS
Test 3 of 3: PASS

Test 583 of 974: 432/583 (74.09948542024014%): success