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数学题,高手来啊~

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发表于 2010-8-4 22:59:36 | 只看该作者 回帖奖励 |倒序浏览 |阅读模式
for every positive even integer n, the function h(n) is defined to be the product of all even integers from 2 to n,inclusive. If p is the smallest prime for factor of h(100)+1, then p is
答案是greater than 40
求思路
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沙发
发表于 2010-8-5 10:36:59 | 只看该作者
这题有被讨论过 以下是某位高人滴答案:

According to the given function,
h(100) = 2*4*6*8*...*100

By factoring a 2 from each term of our function, h(100) can be rewritten as
2^50*(1*2*3*...*50).

Thus, all integers up to 50 - including all prime numbers up to 50 - are factors of h(100).

Therefore, h(100) + 1 cannot have any prime factors 50 or below, since dividing this value by any of these prime numbers will yield a remainder of 1.

Since the smallest prime number that can be a factor of h(100) + 1 has to be greater than 50, The correct answer is E.
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