Okay, so the .NET big integer implementation is like two orders of magnitude slower than it could be? I will have a look into that, I always assumed that all big integer libraries are more or less comparable in performance. Thanks for the hint.
EDIT: I found an issue [1] concerning .NET big integer performance, it seems it is only using pretty basic and relatively slow algorithms, especially for multiplication which is the relevant operation here.
EDIT: I found an issue [1] concerning .NET big integer performance, it seems it is only using pretty basic and relatively slow algorithms, especially for multiplication which is the relevant operation here.
[1] https://github.com/dotnet/runtime/issues/14407