I’m doing the Rectangles and my code goes wrong even though it runs smoothly

import math
def square(n):
n2 = int(math.sqrt(n))
k = 0
a = 0
for i in range(1, n2 + 1)
if n % i == 0:
k = k + int(n/i) - a
a = a + 1
return k
n = int(input())
print(square(n))