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Project Euler 23:Find the sum of all the positive integers which cannot be writt

发表于: 2013-05-16   作者:EmmaZhao   来源:转载   浏览次数:
摘要: A perfect number is a number for which the sum of its proper divisors is exactly equal to the number. For example, the sum of the proper divisors of 28 would be 1 + 2 + 4 + 7 + 14 = 28, which means th
A perfect number is a number for which the sum of its proper divisors is exactly equal to the number. For example, the sum of the proper divisors of 28 would be 1 + 2 + 4 + 7 + 14 = 28, which means that 28 is a perfect number.

A number n is called deficient if the sum of its proper divisors is less than n and it is called abundant if this sum exceeds n.

As 12 is the smallest abundant number, 1 + 2 + 3 + 4 + 6 = 16, the smallest number that can be written as the sum of two abundant numbers is 24. By mathematical analysis, it can be shown that all integers greater than 28123 can be written as the sum of two abundant numbers. However, this upper limit cannot be reduced any further by analysis even though it is known that the greatest number that cannot be expressed as the sum of two abundant numbers is less than this limit.

Find the sum of all the positive integers which cannot be written as the sum of two abundant numbers.

1. compute the sum of the proper divisors
def sumOfDivision(n):
	limit = n/2
	i = 2
	sum = 1
	while i < limit:
		if n %i == 0:
			limit = n /i
			if n /i == i:
				sum += i
			else:
				sum += (i + n/i)
		i += 1
	return sum

2. finding all the abundant numbers
def abundant():
	result = []
	for i in range(1,28124):
		if sumOfDivision(i) > i:
			result.append(i)
	return result

3. compute all the sums of the abundant numbers and the sum of those cannot be written as the sum of 2 abundant numbers
def sumOfNonAbundant():
	sum = 0
	#打表
	result = abundant()
	flag = [False for i in range(28124)]
	l = len(result)
	for i in range(l):
		for j in range(i,l):
			if result[i] + result[j] < 28124:
				flag[result[i] + result[j]] = True
	for i in range(28124):
		if flag[i]  == False:
			sum += i
	return sum

Project Euler 23:Find the sum of all the positive integers which cannot be writt

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