Perfect Numbers and their reciprocals.

  • Context: Undergrad 
  • Thread starter Thread starter Slats18
  • Start date Start date
  • Tags Tags
    Numbers
Click For Summary
SUMMARY

The discussion centers on Perfect Numbers, defined as numbers where the sum of their divisors equals twice the number itself, exemplified by 6. It highlights that the reciprocals of a Perfect Number's divisors also sum to 2, as shown with 6's divisors: 1, 2, 3, and 6. The conversation explores potential relationships between this property and the convergence of the series (1/2)^n to 2 as n approaches infinity, particularly in the context of the divisors of a Perfect Number.

PREREQUISITES
  • Understanding of Perfect Numbers and their properties
  • Basic knowledge of divisor functions
  • Familiarity with series convergence concepts
  • Mathematical notation and proof techniques
NEXT STEPS
  • Research the properties of Perfect Numbers in number theory
  • Explore the concept of divisor functions and their applications
  • Study series convergence, particularly geometric series
  • Investigate relationships between Perfect Numbers and other number classifications, such as Amicable Numbers
USEFUL FOR

Mathematicians, number theorists, and students interested in the properties of Perfect Numbers and their mathematical implications.

Slats18
Messages
46
Reaction score
0
For those who don't know, here's the definition:

A Perfect Number is some number n such that the sum of its divisors is equal to 2n (or just n if you don't count n|n =P )
Ex: Let n=6, and the divisors of 6 are 1,2,3 and 6

1+2+3+6 = 12 = 2*6.

Moving on, there's also the neat fact about them that states that the reciprocals of the divisors will always add up to 2.

Ex: n=6, 1/6 + 1/3 + 1/2 + 1/1 = 2

Now, my question/wonderment: is there any possible relation between this fact, and the summation of (1/2)^n, which converges to two as n approaches infinity?
 
Physics news on Phys.org
Let

[tex]1 < p_{1} < p_{2} < \ldots < p_{2m} < N[/tex]

be all the divisors of [itex]N[/itex] excluding 1 and itself.

Notice that the number of such divisors must be even and that:

[tex] p_{1} p_{2 m} = p_{2} p_{2 m - 1} = \ldots p_{m - 1} p_{m + 1} = N[/tex]

If [itex]N[/itex] is perfect then we also have:

[tex] N = 1 + p_{1} + \ldots + p_{2m}[/tex]

Divide this equality by [itex]N[/itex] and you get:

[tex] 1 = \frac{1}{N} + \frac{p_{1}}{N} + \ldots + \frac{p_{2m}}{N}[/tex]

But, according to the upper equalities:

[tex] \frac{p_{1}}{N} = \frac{1}{p_{2m}}, \frac{p_{2m}}{N} = \frac{1}{p_{1}}, \ldots[/tex]

and we get:

[tex] 1 = \frac{1}{N} + \frac{1}{p_{2m}} + \ldots + \frac{1}{p_{1}}[/tex]

Q.E.D.
 
Last edited:
Thank you for the speedy reply, Dickfore, and thank you on the proof of why the fact holds. But, I'm more interested in the discussion of whether they are related in any way (excluding the trivial), not just proof-wise =)
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 25 ·
Replies
25
Views
4K
  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 26 ·
Replies
26
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 5 ·
Replies
5
Views
3K