Harvard's CS50x on edx is probably the best free and online introduction to CS and programming. It will give you an incredibly strong foundation. [0]
teachyourselfcs has a solid list of canonical resources that are common across many university programs. [1]
The Art of Problem Solving books are great if you want to learn math to a high level, though it isn't strictly necessary. [2]
[0] https://www.edx.org/learn/computer-science/harvard-universit...