[app4soft]

> part of the major was just a couple of calculus and discrete math courses

On Coursera[0] there are a lot of courses on math[1], including on discrete math[2].

[0] https://en.wikipedia.org/wiki/Coursera

[1] https://www.coursera.org/courses?query=mathematics

[2] https://www.coursera.org/courses?query=discrete%20mathematic...

[conformist]

Coursera and MIT OCW are both great. I would also add edx: https://www.edx.org