working with incredibly large numbers in .NET

I'm trying to work through the problems on projecteuler.net but I keep running into a couple of problems.

The first is a question of storing large quanities of elements in a List<t>. I keep getting OutOfMemoryException's when storing large quantities in the list.

Now I admit I might not be doing these things in the best way but, is there some way of defining how much memory the app can consume?

It usually crashes when I get abour 100,000,000 elements :S

Secondly, some of the questions require the addition of massive numbers. I use ulong data type where I think the number is going to get super big, but I still manage to wrap past the largest supported int and get into negative numbers.

Do you have any tips for working with incredibly large numbers?

Consider System.Numerics.BigInteger.

You need to use a large number class that uses some basic math principals to split these operations up. This implementation of a C# BigInteger library on CodePoject seems to be the most promising. The article has some good explanations of how operations with massive numbers work, as well.

Also see: Big integers in C#