‘‘‘
Project Euler: Problem 21: Amicable numbers
Let d(n) be defined as the sum of proper divisors of n
(numbers less than n which divide evenly into n).
If d(a) = b and d(b) = a, where a ≠ b, then a and b are an amicable pair
and each of a and b are called amicable numbers.
For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110;
therefore d(220) = 284.
The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.
Evaluate the sum of all the amicable numbers under 10000.
Answer: 31626
‘‘‘

def d(n):  #计算数字n所有真因数之和
    res = 0
    for i in range(1, n//2+1):
        if n/i == float(n//i):
            res += i
    return(res)

lst = []  #亲和数列表
for i in range(1, 10000):
    a = d(i)
    b = d(a)
    if b == i and b != a:
        lst.append(i)

res = 0  #所有亲和数之和
for i in range(len(lst)):
    res += lst[i]
print(res)