Not in a hurry. In principle, here's what you have to do. (This procedure is especially useful when you're letting a computer do it. I've examined all of
the numbers up to several million this way):
Check every integer, from 2 up to 1/2 of the number you're wondering about.
For each one, divide it into the number you're wondering about, to see whether
the smaller number is a factor of the bigger one.
If you make it all the way from 2 up to 1/2 of the big number without finding
a factor, then the big number is prime.
