I want to implement an RSA cryptosystem algorithm for a university project and I' m trying to decide which programming language to use. I am very familiar with C so it would be a convenient choice. However, the algorithm will have to deal with very large numbers (it will include a Primality subroutine), and I have heard that using Python will result in a better implementation. Is that right? 
Thank you in advance.
I don't know if Python will result in a "better" implementation, since better is rather subjective here. You can find numerical libraries for both that will allow you to deal with large numbers easily. Python has the advantage (imo) of having the numpy library which is very easy to read and use and is generally more human readable which often leads to easier debugging.
Suitable Language for RSA implementation