Free Math Textbooks
These are books that i've verified them in one way or another. Some i've read and consider good, some i checked up the author and is reputable mathematician, some are well known professors i know of, etc.
Elementary Number Theory by W Edwin Clark (highschool readable)
An Introduction to the Theory of Numbers by G. H. Hardy, Edward M. Wright, Andrew Wiles. Buy at amazon
Elementary Number Theory by Underwood Dudley Buy at amazon
Introduction to Probability, by Charles M Grinstead, J Laurie Snell Shoup (highschool readable)
Abstract Algebra by David S., Foote, Richard M Dummit Buy at amazon
Functional Geometry, 2013, Sussman, Wisdom, Farr (undergrad)
Mathematical Logic, by Stephen G Simpson (graduate)
Foundation of Math, by Stephen G Simpson (graduate)
Homotopy Type Theory (graduate)
the following i have not verified.
If you have a question, put $5 at patreon and message me.