The set of odd numbers is countably infinite, i.e. it can be put into one-to-one correspondence with the natural numbers by the formula 25(2n-1) for n ≥1. This may not seem reasonable if this is your first exposure to questions about infinity...but if so, you will need to explore this topic a bit and ultimately look into the mathematics invented by G. Cantor.
The formula I gave you is NOT correct. The correct formula is 23+2n for n≥1. The rest of the answer is correct. I apologize for my error!
