Sometimes students will contact me, as my email is visible. This time, an undergraduate in Sri Lanka has no number theory courses available and is self-studying.
My own experience is that it helps to run computer experiments; that is how I learned the topic. I took a course in C++ some twenty years ago, and that has served me well. Steep learning curve, though. It helped a good deal when I found I could use the GMP library for large integers. My impression is that many current computer languages have large integers built in.
What computer languages might one recommend for, say, investigations in number theory?
As far as books, she is currently reading Burton. I have requested that and Burn, A Pathway into Number Theory, from my library. The one thing I would add to early number theory is quadratic forms, maybe just binary, before attempting quadratic fields. I like that Burns does the automorphism group of a binary quadratic form; he may not call it a group, not sure yet.