Sum of odd numbers using while loop in python

Question

I'm new to programming, I was asked to use a while loop to add all odd numbers between 1 and (2*n)-1.

def sum_odd_n(n):
    while n<2*n:
        sum = 0
        if n%2==1:
            sum = sum+n
    return (sum)

I cannot find my mistake. Please help