A friend of mine who knows more mathematics that I do, told me that nowadays number theory is basically about studying prime numbers.
I'm under the impression that solving diophantine equations and cryptography for example are subfields of number theory.
I'm under the impression that although at first glance these subfields dont seem to have anything to do with prime numbers, prime numbers play a central role in them. (is this true?)
So it seems that in certain subfields of number theory that aren't directly about prime numbers, the researchers study and tackle their problems by studying prime numbers, and so prime numbers would be central in such subfields.
So I'm asking for examples of subfields of number theory that don't rely heavily/aren't prime number focused.