[問題]PP-T1-DS3

[amyliang]

3.196-!-item-!-187;#058&000141
How many different prime numbers are factors of the positive integer n ?
(1)Four different prime numbers are factors of 2n
(2)four different prime numbers are factors of n^2

ans:B

why? 我對prime number真的一點都不了解
我知道prime number的因子就是 1跟自己
可是 這樣為什麼就(2) 就可以成立了呢
就像拿5*7*11*13 也不可能變成某數的平方啊??
誰可以告訴我 為什麼(2)成立呢?如何算出來的呢?

[小花]

請參考
http://www.formosamba.com/phpBB3/viewtopi ... me+numbers