Will Jagy

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The two excellent number theory books I keep recommending (for self study or help with the basics) are Weissman: An Illustrated Theory of Numbers. Lehman: Quadratic Number Theory: An Invitation to Algebraic Methods in the Higher Arithmetic. The web pages are

https://bookstore.ams.org/mbk-105/

https://bookstore.ams.org/dol-52/