Thanks! I'm the 3rd scenario in my case, and I joined that Brilliant website. It seems to be helpful so far. I do have to participate in classes where I know everything, so what I'll end up doing most of the time is having my dad send me to school with special math worksheets that are at my level that I can do during math class.

I already have some Martin Gardener books, and will be ordering more, as you are not the only person who recommended him.