# Countable Sets

1. Apr 29, 2010

### Dustinsfl

F is all integers that are multiplies of 5

$$f(n) = \begin{cases} 0, & \mbox{if }n\mbox{ 1} \\ \frac{5n}{2}, & \mbox{if }n\mbox{ is even}\\ ? , & \mbox{if }n\mbox{ is odd} \end{cases}$$

N exists in the natural number
I don't know how to obtain the function that will represent the odd integers.

Last edited: Apr 30, 2010
2. Apr 30, 2010

### Gib Z

Are you trying to get a function that produces all the integer multiples of 5?

Whats wrong with f(n) = 5n ?

3. Apr 30, 2010

### Dustinsfl

I forgot to mention n exists in the natural numbers.

4. Apr 30, 2010

### Gib Z

Ok then, the n is even part of your function will give all the positive multiples, now try something similar for n odd. I don't know how to give you a decent hint without giving it away, but basically, the odd case is very similar to the even case, except with a negative sign, and a little change to the n term to make sure it's divisible by 2.