This is a list of number theory topics, by Wikipedia page. See also list of cryptology topics.
17.1 Number sequences 17.2 Prime and related sequences 17.3 Magic squares, etc.
Main articles:Computational number theory, algorithmic number theory
See list of algebraic number theory topics
NB Listing here is not pejorative, since many famous topics in number theory have origins in challenging problems posed purely for their own sake. See recreational mathematics.