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标题: PREP2-DS-60 [打印本页]

作者: shuangyuym 时间: 2009-7-31 07:08 标题: PREP2-DS-60

Does the integer k have a factor p such that 1 < p < k ?

(1) k > 4!

(2) 13! + 2 <= K <= 13! + 13

答案(B), 求教~谢谢!!

作者: nickynicky 时间: 2009-7-31 22:05

(1)k > 4!= 24 if k =29, a prime number, then k has no factor between 1 and itself
(2)13! = 1*2*3*...*13. so if k is an interger between 13! +2 and 13!+13, inclusive, k definitely has a product smaller than k. i.e. k = 13!+5 = 5 * (1*2*3*4*6*...*13+1) so k has a factor 5 such that 1<5<k

作者: shuangyuym 时间: 2009-8-1 08:56

got it. thanks so much.

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