Just be patient. Posting your question over and over again will not get you replies any faster. Also, in the future, it's much better if you start your own topic. On the top right corner of the forum index, there is a "Post new topic" button. Click that.
As for your question, I'm not entirely sure what you mean. The odd numbers can be represented by the set:
Which basically means all the numbers such that they can be written in the form 2k + 1 where k is an integer. So for example:
1 = 2*0 + 1
3 = 2*1 + 1
5 = 2*2 + 1
25= 2*12 + 1
But you can't have 24 because:
24 = 2*11.5 + 1 but 11.5 isn't an integer.
Now if you wanted only from 1 to 80, then you would have:
That additional 0 ≤ x ≤ 80 makes it so x can't be -3 or 255, or any other number outside the bounds.
Is this what you were asking?
"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."
I don't think I understand it.
A main property of the prime numbers is that there don't exist a fast mathod for predicting wheter a number is prime or not.
IPBLE: Increasing Performance By Lowering Expectations.