Ok, looking back at the original post I'm nearly regretting it as I need to find the time to actually write these - but at least this one was quick and simple. In fact it may be too simple to use as a tech test, but anyways here it is.

A prime number is any number greater than 1 which is only divisible by itself and 1. The method I use here simply checks all the values up to the number under investigation to see if division by them would leave a remainder of zero. There are probably faster ways to do this using smarter maths, and if you know of one, please post a comment!