The C#9 example is preferable as it is easiest to read for most developers regardless of their background.
If you are capitated to using an earlier framework that doesn't allow for this syntax then use the format that got over 800 votes.
The prime number example while good academically speaking is an unrealistic business case, I seriously doubt that the over 800 respondents have had a need to find prime number ranges (yes I know it's just an example) and switch between them for their day to day programming.
Lambda expressions and LINQ syntax (less so) examples, while cool, are difficult to read for the uninitiated.
Who knows, maybe Microsoft will add a 'between' keyword in future versions of C# to make ranges easier to read -- that I'd like to see!
Until such time, the C#7 and updated C#9 examples below for ranges work and look best for readability.