http://blogs.msdn.com/b/dboyle/archive/2013/03/08/checking-for-a-prime-number.aspxOk, 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 numberen-USTelligent Evolution Platform Developer Build (Build: 5.6.50428.7875)http://blogs.msdn.com/b/dboyle/archive/2013/03/08/checking-for-a-prime-number.aspx#10410476Fri, 12 Apr 2013 00:51:08 GMT91d46819-8472-40ad-a661-2c78acb4018c:10410476Comet<p>If you are looking for clever maths, then see the &quot;Agrawal–Kayal–Saxena primality test&quot; as a &nbsp;general, polynomial, deterministic, and unconditional algorithm. &nbsp;If a candidate can explain it to you, then they are a &quot;prime&quot; candidate. &nbsp;;-)</p> <div style="clear:both;"></div><img src="http://blogs.msdn.com/aggbug.aspx?PostID=10410476" width="1" height="1">http://blogs.msdn.com/b/dboyle/archive/2013/03/08/checking-for-a-prime-number.aspx#10410473Fri, 12 Apr 2013 00:39:16 GMT91d46819-8472-40ad-a661-2c78acb4018c:10410473Comet<p>You can go twice as fast, if you have a separate test for divisibility by 2, and iterate over the odd numbers as test divisors.</p> <p>You can finish your testing by an exponent of .5; namely, once your test divisor exceeds the square root of your candidate prime, you can terminate your loop.</p> <div style="clear:both;"></div><img src="http://blogs.msdn.com/aggbug.aspx?PostID=10410473" width="1" height="1">