Perfect Number & Prime-saturated number

[Grace]

1. Whick of the followingis a pefect number , if a perfect is a number equals the sum of tall its positive divisors less than the number itself?

A) 16
B) 18
C) 20
D) 24
E) 28


這題答案是E, 我不懂 什麼 是perfect number???? Help~


2. A positive integer is a prime-saturated number if it is not equal to 1 and has no prime facotr large than or equal to the suqare root of the number itself. Which of the following is a prime-saturated number?

A) 15
b) 21
C) 44
D) 68
E) 70

這題答案是E, 我不懂 什麼 是perfect saturated number???? Help~

[bear]

1.perfect number的意思就是 把小於這個數的所有因數全部加起來,會等於這個數
舉例
A) 16 -> 小於16的因數有 1,2,4,8 ,通通加起來等於15
--> 不等於16 , 所以不是perfect number

2.prime-saturated number 的意思就是 這個數的質因數(不等於1)都要小於這個數的根號 的數字
舉例
A) 15 --> 15的質因數有 3,5 , 其中5大於 根號15 (約3.87) , 所以不是prime-saturated number

[Grace]

熊妹~
實在太感謝你這麼清楚的解釋 我懂了~~
感恩喔~ ;)