I\'m reviving this question, and making it more specific: Is there a .NET framework library that supports numbers with arbitrary digits of precision?
There are a few options here.
A good option is W3b.Sine, which is native C#/.NET, and supports arbitrary precision floating point values.
If you are only dealing with integer values, IntX provides support for arbitrary precision integer values. A potentially more mature option would be C# BigInt, but again, this will not support floating point operations.