kainster

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怎么就不对了呢

Posted on 2008-10-28 12:58 kainster 阅读(143) 评论(0)  编辑  收藏

For a positive integer n, let σ2(n) be the sum of the squares of its divisors. For example,

σ2(10) = 1 + 4 + 25 + 100 = 130.

 

Find the sum of all n, 0 n 64,000,000 such that σ2(n) is a perfect square.

using System;
using System.Collections.Generic;
using System.Text;

namespace Prob211
{
    class Program
    {
        const int NUM = 64000000;
        // 为了方便，values数组从1开始计数
        static long[] values = new long[NUM ];
        // 验证某个数是不是完全平方数
        static bool IsPerfect(long num)
        {
            long sq = (long)Math.Sqrt(num);
            
            if (sq * sq == num)
                return true;
            return false;
        }
        static void Prob211()
        {
            for (int i = 0; i < values.Length; i++)
                values[i] = 0;
            long sum = 0;
            for (int i = 1; i < values.Length; i++)
            {
                long num = i;
                // 对于i的每个倍数都加上 i*i
                while (num < values.Length)
                {
                    values[num] += i * i;
                    num += i;
                }
                // 判断当前数是否是完全平方数
                if (IsPerfect(values[i]))
                {
                    sum += i;
                    Console.WriteLine(i + ":" + values[i]);
                }
            }
            Console.WriteLine(sum);

        }
        static void Main(string[] args)
        {
            Prob211();
            Console.Read();
        }
    }
}

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