Euler problem 3 is about prime factors, otherwise finding the largest divisor would be a bit too trivial. The problem might look intimidating, but I suppose it can be solved with simple trial division. You definitely don't need an array that large, and whatever programming language, the memory usage would be too large.For example, the factors of 30 are 1, 2, 3, 5, 6, 10, 15, 30.
(Tried at ideone.com, Python with trial division by odd integers yields the answer in 0.03 seconds without any array. It only comes down to getting the algorithm right.)
