# Is infinity even or odd?

1. Feb 28, 2005

### Icebreaker

Is infinity even or odd? If it's even (or both), then it would mean there's a finitely largest prime.

By coarsely applying limit concepts, and lim(x->inf)x/2 does not yield a remainder.

2. Feb 28, 2005

### cepheid

Staff Emeritus
I'm no math Phd, but I do know this: infinity is not a number!

3. Feb 28, 2005

### z-component

Infinity isn't a number; it's a concept used in mathematics.

4. Feb 28, 2005

### Icebreaker

So, what, we can assume that there will ALWAYS be larger primes?

5. Feb 28, 2005

### cepheid

Staff Emeritus
You shouldn't assume anything in math. I seem to remember seeing a proof of that somewhere, but I can't remember any of the details. My memory could be wrong. Surely somebody will know though...

6. Feb 28, 2005

### Hurkyl

Staff Emeritus
Suppose there are finitely many primes. Can you find a number divisible by all of them? Can you find a number not divisible by any of them?

7. Feb 28, 2005

### Chronos

Interesting. Is hydrogen male or female? The answer is similar.

8. Feb 28, 2005

### Icebreaker

Wouldn't the question be: suppose there are finitely many primes, can a combination of their products be used to construct any integer?

9. Feb 28, 2005

### Hurkyl

Staff Emeritus
Would the answer to this answer your version?

10. Feb 28, 2005

### mathwonk

infinity = 2 times infinity, hence infinity is even, which may seem odd. :tongue2:

11. Mar 1, 2005

### shmoe

It's even odder since infinity=2*infinity+1, hence it's odd as well as even. (joking :tongue2:)

Seriously though, infinity is not a number that you can perform arithmetic with. You can add it to the reals and make what's often called the extended reals, but don't expect it to play nice with the rest of the numbers. Certainly don't expect it to have any nice properties like even or odd.

12. Mar 1, 2005

### Icebreaker

What is the answer?

13. Mar 1, 2005

### matt grime

Not every number can be formed from a product if primes if there were only a finite number of them: multipply them all together and add 1.

14. Mar 1, 2005

### shmoe

The answer is yes. If you can find a number not divisible by all the primes, then you would have found a number that is not a combination of their products.

Suppose their are finitely many primes, $p_1,p_2,\ldots,p_n$. Then consider their product $M=p_{1}p_{2}\ldots p_{n}$. Then M is divisible by all the primes. This answers Hurkyl's first question (from post#6). Can you use it to answer the second?

edit:I type slower than matt!

15. Mar 3, 2005

### moving finger

In another thread on this forum I've seen posts claiming that an integer cannot be infinite (ie only finite integers are allowed).

See https://www.physicsforums.com/showthread.php?p=478006#post478006

Any thoughts on this subject anyone?

If an infinite integer is allowed, then it must also have an infinite number of digits, right?

16. Mar 3, 2005

### matt grime

They aren't elements of $$\mathbb{Z}$$ or $$\mathbb{N}$$ by definition so your argument is baseless.

You are saying: if we assume that when cantor said the natural numbers he actually meant something entirely different then his argument is wrong. As he didn't mean something entirely different his argument is correct and you are wrong.

Last edited: Mar 3, 2005
17. Mar 3, 2005

### evthis

infinity is a description not a numerical value and since only numerical values can be odd or even, infinity is neither.

18. Mar 9, 2005

### HallsofIvy

Is green even or odd? Is salt even or odd? Is Fred even or odd? (Oops, bad example, Fred is definitely odd!)

The point is that "infinity" is not a member of the set of integers and that is all the terms "even" or "odd" (in the mathematical sense) apply to.

19. Mar 9, 2005

### penguinraider

If infinity could be reguarded as a number, I think it would e both. It would also be the only number bigger, smaller and the same size as itself at the same time. This is because infinity is not a number. If we were to fill infinity with the highest known number, it would still fall short. Therefore infinity would have to e flled with every impossible number (including decimals). That is the only way it would come close to becoming a "proper" number.

20. Mar 9, 2005

### BobG

Hydrogen is kind of like "Pat What's That".

Potassium, on the other hand, is male, while Chlorine is female.

#### Attached Files:

• ###### Positive Alkali Metals.JPG
File size:
36.1 KB
Views:
277
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook