http://togetter.com/li/875421 の解答（Python3）

stepup.py

import math

n = int(input())
n2 = n * 2
max = math.floor(math.sqrt(n2))
arr = []
for i in range(2, max + 1):
    if n2 % i == 0:
        j = n2 // i
        if i % 2 == 0 and j % 2 == 1:
            arr.append((j + 1) // 2 - i // 2)
        if i % 2 == 1 and j % 2 == 0:
            arr.append(j // 2 - i // 2)
print(sum(arr))