If the sum of the divisors of a positive integer n excluding n itself is equal to n, then n is called a Perfect Number. Which of the following is NOT a Perfect Number?
(A) 6
(B) 28
(C) 124
(D) 496
(E) 8128
5-Day Free Trial
5-day free, full-access trial TTP
Available with Beat the GMAT members only code
MORE DETAILS
n excluding n itself
This topic has expert replies
-
sanju09
- GMAT Instructor
- Posts: 3650
- Joined: Wed Jan 21, 2009 4:27 am
- Location: India
- Thanked: 267 times
- Followed by:80 members
- GMAT Score:760
Last edited by sanju09 on Sat Mar 06, 2010 6:26 am, edited 1 time in total.
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
-
rohan_vus
- Master | Next Rank: 500 Posts
- Posts: 189
- Joined: Thu Apr 03, 2008 2:03 pm
- Location: USA
- Thanked: 21 times
Should be A
Trying with 4 gives 1 and 2 as possible factors and it tells that 4 is not a perfect number
Sum of all factors of a perfect square (say n ) including n istelf is always odd . So sum of all factors factors excluding n is also always odd if n is even
So a even perfect square is never a perfect number .
Trying with 4 gives 1 and 2 as possible factors and it tells that 4 is not a perfect number
Sum of all factors of a perfect square (say n ) including n istelf is always odd . So sum of all factors factors excluding n is also always odd if n is even
So a even perfect square is never a perfect number .
-
sanju09
- GMAT Instructor
- Posts: 3650
- Joined: Wed Jan 21, 2009 4:27 am
- Location: India
- Thanked: 267 times
- Followed by:80 members
- GMAT Score:760
Please see it again as I have edited it in the meanwhile, sorry for inconvenience.rohan_vus wrote:Should be A
Trying with 4 gives 1 and 2 as possible factors and it tells that 4 is not a perfect number
Sum of all factors of a perfect square (say n ) including n istelf is always odd . So sum of all factors factors excluding n is also always odd.
So a perfect square is never a perfect number .
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
