When generating random integers in .NET, the goto is the Next() method of the Random class.

var randomNumber = Random.Shared.Next();

Console.WriteLine(randomNumber);

This will print something like this:

34234234

This, however, just gives you a 32 bit integer int, bounded from int.MinValue (-2,147,483,648) and int.MaxValue (2,147,483,648)

What if you wanted a larger number, a 64-bit integer - Int64 (or long).

This is bounded by long.MinValue (-9,223,372,036,854,775,808) and long.MaxValue (-9,223,372,036,854,775,808)

Integral types and their sizes are covered in the post The Other Integer Types

The Random class supports this via the NextInt64() method.

var randomNumber = Random.Shared.NextInt64();

Console.WriteLine(randomNumber);

This will print something like this:

8588670651705391622

TLDR

The Random class supports generation of 64 bit integers using the NextInt64() method.

Happy hacking!