Show that the set of all integers which are divisible by 3 is countable.
问题描述：
Show that the set of all integers which are divisible by 3 is countable.
大致就是证明 能被3整除的数的集合是可数的,求详解
答
被3整除的数n=3k,k∈Z,因为整数集是可数集,所以3k也是可数集
只要建立一一对应即可