I am kind of new to this problem and I tried solving it with open mind. Please don't be judgmental, this is what I got.
Let us assume, for the sake of contradiction, that the Collatz conjecture is false and that there exists a cycle in the Collatz sequence other than the well-known $4-2-1$ loop. ...
I voted to close this question as a duplicate, but my target was not really a duplicate, and I had to withdraw my vote. Now, I can't vote again to close it. Please vote to close it as a PSQ.
Please reopen Introductory Group theory textbook.
It's illogical for this to be closed as "opinion-based", when introductory textbook recommendations remain open.
Books on Number Theory for Layman
Good Book On Combinatorics
What is the best book to learn probability?