請教GWD19-29

[amos55]

(B)2n is divisable by twice as many positive interger as n
我看不太懂題目
答案就是B
題目是要問N是ODD嗎??

[scujean]

Q29:
Is the integer n odd?
(1) n is divisible by 3.
(2) 2n is divisible by twice as many positive integers as n.

條件2→能整除2n的正整數個數/能整除n的正整數個數=2
假設n=3,奇數
2n=6可被1, 2,3,6共4個正整數整除
n=3可被1,3共2個正整數整除
假設n=4 ,偶數
2n=8可被1,2,4,8共4個數整除
n=4可被1,2,4共4個數整除
當n為偶數時,不符題幹,可以確定n為奇數

麻煩下次把題目PO齊..