Help Regarding Number Theory for Competitive Programming

Hi, I want to study Number Theory as it’s an important topic for competitive programming. And I know some basic number theory. When I google search for Number Theory there lots of resources which is available on the Internet after seeing that I am just confused what to study??. So please help me with selecting the right resources.

Please somebody give me the resources that can really help me.

  1. https://www.codechef.com/certification/data-structures-and-algorithms/prepare

  2. https://cp-algorithms.com/

for more guidance you can watch this video(hindi) :- https://www.youtube.com/watch?v=gREDFgHL9m4

Thanks bro.