53. 证明一个数x是不是prime number 条件1:3x+1是prime number 条件2:5x+1是prime number
69. K是正整数,5^K是99到199所有奇数乘积的factor,问K最大可能是多少。
147. N is interger, reminder is 1 when divided by 4, remidner is 2 when divided by 3, how many of N is under the following range A) 9.5 to 16.5 B) 17.5 to 20 sth C) 20sth to 30 sth D) E) 161. PS 给出一个函数,分子是(x-1)的根号,分母是x+1,问这个函数的定义域(domain) 一开始没仔细读题,看成求函数值的范围,浪费了点时间. 答案应该是x>=1