首页
登录
职称英语
Which of the following cannot be expressed as the sum of two prime numbers?A、21
Which of the following cannot be expressed as the sum of two prime numbers?A、21
游客
2025-02-27
10
管理
问题
Which of the following cannot be expressed as the sum of two prime numbers?
选项
A、21
B、14
C、18
D、28
E、23
答案
E
解析
这道题目用排除法当然可以迅速解出来,比如:21=19+2,14=7+7,18=13+5,28=23+5,只剩下23,当然选择E。但是如果利用上面的定理,则速度更快。五个选项中B、C、D都为大于2的偶数,根据定理必然可以表达为两个质数的和;剩下选项A、E均为奇数,若两数相加为奇数,则这两数必然为一奇一偶。而这个数又要能够表达为两个质数的和,那么必须这一奇一偶都为质数,我们知道在所有质数中2是唯一的一个偶数,因此若A或E能够表达为两质数的和,其中一个一定为2,选项A:21-2=19,E:23-2=21,19为质数,21=3×7不为质数,因此E是正确答案。
转载请注明原文地址:https://tihaiku.com/zcyy/3974524.html
相关试题推荐
Forallrealnumbersx,theoperationx*isdefinedbytheequationx*=x+4,If(
WhichofthefollowingnumbersisNOTthesumofthreeconsecutiveoddintegers?
Therearefivepositivenumbersn+2,n+1,n-2,nandn+9,whichofthefollowing
Thepassageasawholecanbestbecharacterizedaswhichofthefollowing?[br]
Thepassageasawholecanbestbecharacterizedaswhichofthefollowing?[br]
Thepassageasawholecanbestbecharacterizedaswhichofthefollowing?[br]
Whichofthefollowingmostaccuratelystatesthemainideaofthepassage?[br]
Whichofthefollowingmostaccuratelystatesthemainideaofthepassage?[br]
Whichofthefollowingmostaccuratelystatesthemainideaofthepassage?[br]
Whichofthefollowingwouldmostlogicallybethetopicoftheparagraphimmedi
随机试题
Attheparty,everybodycongratulatedthescientist______winningtheawardafte
Inanoldtownlivedamerchant.Heearnedhugeprofitsbyfairmeansandfo
Manyoftoday’scollegestudentsaresufferingfromaformofshock.Lisais
对于一个B类网络,可以分配(4)个主机地址。A.1022 B.4094
混凝土构件的测试一般选用标距为100mm左右的应变片,且标距不宜小于2~3倍的最
用水浸法测定沥青与矿料的黏附性试验中,按每100g矿料加入沥青5.5g±0.2g
强心苷治疗心房纤颤的主要机制是()。A.降低窦房结自律性 B.缩短心房有效不
(2022年真题)某社会工作服务机构在开展老旧社区治理项目时,发现一些高龄老人家
传统的人事管理被新型的人力资源管理所替代的具体表现是( )。A.人事管理的范畴
项目目标控制的主要措施有()。A.组织措施 B.管理措施 C.经济措施 D
最新回复
(
0
)