It's been fun reading responses in the last two Project Euler threads. If you missed them, you can view Problem #1 and Problem #2.
Let's keep it rolling with Problem #3. Again, this is from the wonderful Project Euler.
The prime factors of 13195 are 5, 7, 13 and 29.
What is the largest prime factor of the number 600851475143 ?
Look forward to seeing solutions in your language of choice!