# Every other odd number representation

1. Jul 27, 2014

### Maylis

Hello,

Is there any formula that describes every other odd number, for $n = 1,2,\dots$? I can't seem to find anything that does it on the web.

Something that would do 1,5,9,13,...

2. Jul 27, 2014

### bhillyard

Try 2n - 1
2n guarantees even
Subtract 1 produces an odd number.

3. Jul 27, 2014

### Maylis

yeah but I said every other odd, not every odd

4. Jul 27, 2014

### sjb-2812

4n-3? Or am I missing something really obvious?

5. Jul 27, 2014

### AlephZero

If "2n + something" gives a series of numbers separated by 2, what do you think gives a series separated by 4?

EDIT: Oh well, I was trying to get you to think it out for yourself, but somebody else just told you the answer.

6. Jul 27, 2014

### HallsofIvy

Staff Emeritus
Then 4n- 3 of course. (4n- 1 gives the other odd numbers, 3, 7, 11, etc.)

7. Jul 27, 2014

### HallsofIvy

Staff Emeritus
Note that the last three of us, essentially saying the same thing, posted within 2 minutes!