Prep-PS-7

chanyeen

7.        905-!-item-!-187;#058&000575
For every positive even integer n, the function h(n) is defined to be the product of all the even integers from 2 to n, inclusive.  If p is the smallest prime factor of h(100) + 1, then p is

(A) between 2 and 10
(B) between 10 and 20
(C) between 20 and 30
(D) between 30 and 40
(E) greater than 40
答案是E why？

pansy

如果小于40的prime，总能在h(100)中找到的它的倍数把它约掉，这样这个prime肯定就不是h(100)+1的factor了，所以一定要找大于40的prime才可能成为h(100)+1的factor

myice

回复 4# s


    s真好呀

hellokitty

回复 4# s


    不错不错

s

回复 1# chanyeen


   我找到了，你可以看看之前的讨论
http://forum.topway.org/viewthre ... highlight=Prep-PS-7

s

回复 2# hellokitty


    哈哈，同感

hellokitty

之前好像有人问题这题？