#21.py

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#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.
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def d(n):
    # Return the sum of proper divisors of n
    divisors_sum = 0
    for i in range(1, n):
        if n % i == 0:
            divisors_sum += i
    return divisors_sum

def solve():
    # Iterate over the integers from 1 to 9999
    amicable_numbers_sum = 0
    for a in range(1, 10000):
        b = d(a)
        if a != b and d(b) == a:
            amicable_numbers_sum += a
    return amicable_numbers_sum

print(solve())