Write the biggest prime

Question

I'm trying to solve the biggest prime programming praxis problem in C#. The problem is simple, print out or write to file the number: 2^57,885,161 − 1 (which has 17,425,170 digits)

I have managed to solve it using the amazing GNU Multiple Precision Arithmetic Library through Emil Stevanof .Net wrapper

var num = BigInt.Power(2, 57885161) - 1;
File.WriteAllText("biggestPrime.txt", num.ToString());

Even if all the currently posted solutions use this library, to me it feels like cheating. Is there a way to solve this in managed code? Ideas? Suggestions?

PS: I have already tried using .Net 4.0 BigInteger but it never ends to compute (I waited 5 minutes but it is already a lot compared to 50 seconds of the GMP solution).

Answer 1

It's also more a cheat than a solution but I solved this using the IntX library

IntX.Pow(2, 57885161, MultiplyMode.AutoFht) - 1;

It ran approximately 6 minutes. Still this is not a real answer though. Would be interesting to see something "real".

EDIT: Using a C# Stopwatch I figured that the calculation only took 5 seconds, it's the process of ToString that takes extremely long.