<p>Probably all books written by Titu Andreescu and Paul Zeitz are “legit” (from personal experience). I’m not sure about the rest, but they should all be fine.</p>
<p>^agree. .</p>
<p>Terence Tao’s book is also probably “legit” as he’s the genius of the century (in my opinion). I would look through the books of the aforementioned authors and that of Terence first.</p>
<p>Thank you…</p>