'''

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)