I’ve looked around this site and the web quite a bit, but can’t find a definitive answer on whether or not the secret key $k$ used in the AES crypto-system has to be a prime number? Or can you just use any random values for the $128,192$ or $256$ bit long keys?

As a personal educational exercise, I’m working on my own implementation of AES, but my only other crypto experience is with the RSA crypto-system, though rather an elementary understanding, where the keys need to be prime, so I guess I just assumed the key for AES did as well. From what I gather the answer is “no”, but I don’t know enough about AES yet, to know whether or not that makes any difference?