Are There Numbers That Are Slightly Excessive?

  • Thread starter Thread starter **bouncey!!**
  • Start date Start date
  • Tags Tags
    Numbers
Click For Summary
SUMMARY

The discussion centers on the existence of slightly excessive numbers, also known as quasiperfect numbers, defined by the equation σ(n) = 2n + 1, where σ(n) represents the sum of divisors of n. Participants argue that quasiperfect numbers must be even, as odd numbers cannot yield the required sum of factors. The conversation highlights the complexity of proving the existence of such numbers, with references to mathematical properties and the ongoing open problem regarding their existence. Key points include the distinction between proper divisors and total divisors, and the assertion that all powers of 2 are slightly defective.

PREREQUISITES
  • Understanding of divisor functions, specifically σ(n)
  • Familiarity with the concepts of perfect and excessive numbers
  • Basic knowledge of number theory, including factorization
  • Ability to work with mathematical proofs and definitions
NEXT STEPS
  • Research the properties of quasiperfect numbers and their implications in number theory
  • Study the divisor function σ(n) and its applications in identifying perfect numbers
  • Explore the relationship between odd perfect squares and quasiperfect numbers
  • Investigate the proof that all powers of 2 are slightly defective
USEFUL FOR

Mathematicians, number theorists, and students interested in advanced number theory, particularly those exploring the properties of quasiperfect and excessive numbers.

  • #31
It should be \sigma(2^k)=2^{k+1}-1. this tells youe 2^k can't be quasiperfect right?

So what about 2^k n where n is odd? If this is quasiperfect, can you say anything about n?
 
Physics news on Phys.org
  • #32
genii not geniuses said:
if k = 4 then sigma(2^k) = 15

16 is a divisor of 16.
 
  • #33
I follow you now but I don't know what I can say about n.
 
  • #34
Can you say anything about \sigma(2^k n)? You know it must be odd if this is quasiperfect...
 
  • #35
well sigma(2^k*n) is even.
 
  • #36
genii not geniuses said:
well sigma(2^k*n) is even.

What makes you say that?
 
  • #37
Well, isn't the sum of the divisors of an even number always even?
 
  • #38
genii not geniuses said:
Well, isn't the sum of the divisors of an even number always even?

No...\sigma(2)=3, \sigma(18)=\sigma(2)\sigma(9)=3\times 13=39
 
  • #39
Ohhhhhh... I'm used to not counting the number itself, which is why I keep getting confused.
 
  • #40
sigma(2^k * n) = odd
 
  • #41
genii not geniuses said:
sigma(2^k * n) = odd

\sigma(6)=12

get used to counting the number itself. This sigma I've defined is the standard version across number theory texts.

You know that \sigma(ab)=\sigma(a)\sigma(b) when a and b are relatively prime right (i.e. sigma is multiplicative)? Use this fact here.

I'm thinking we may be in trouble later on though, do you know about Quadratic Reciprocity?
 
  • #42
No, explain please!
 
  • #43
genii not geniuses said:
No, explain please!

I think you should get yourself a book with "elementary/introductory number theory" in the title and get to work. Head over to the "Number Theory" section of this website, there's a few threads posting book suggestions. get one (or several) and post questions there. This isn't really the best format for several number theory lectures (nor do i have the time), but we can definitely help you with sticking points as they come up.
 
  • #44
ok, thanks!
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
Replies
3
Views
2K
Replies
6
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 3 ·
Replies
3
Views
1K