I can tell you to look for the courses of
Calculus Single Variable and
Calculus Multivariables from MITs OCW MOOC offering. I have found both self-paced courses excellent and very helpful to refresh my decade old mathematics studies as a preparation to take the
Linear Algebra Course presented by Prof. Gilbert Strang. Prof. Strang has written an excellent book that represents the "readings" for both Calculus courses. The book is for free and legal as a
pdf.
The combination of the excellent book from Gilbert Strang and the 2 equally brilliant OCW courses I have supplied you the link to did get me more up to speed so that I guess I know more today then I did know as a high school freshman in Germany! I did also investigate what is a basic knowledge required for any math intensive study and I came the conclusion they are:
1. Linear Algebra: Here the course from Gilbert Strang is excellent, the video recordings of his lectures are those of real expensive MIT courses!
2. Analysis I and II: I have selected a video recording of the lectures from a professor Groth from the University of Tübingen, because I did like his way of teaching. His course builds upon 2 books written by Prof. Terence Tao from a university in California. He help the courses for Analysis 1 & 2 as course with Honor and his books are the readings for it. I remember quite a time ago I searched for his personal webpage and there it was possible to download free and legal the 2 books.
Having had some talks with a mathematics professor from the technical university of Munich, Mathematical institute, during an "Information Event"! I praised both the course from Prof. Groth and Prof Terence Taos way to address Analysis. I did like that both follow a very stringent methodology starting from the "Number Theory". The message I got from him was, that after a french anonymous group of mathematicians did work over decades on bulding the whole mathematics starting from the number theory today "structures" were the approach of mathematics. When you watch and listen to the video recording Dr. Keith Devlin I showd in my earlier contribution, a YouTube, he defines that mathematics is the study of structures. It toook me about a year to investigate what the Prof from the Munich University meant when he taught about structures and I found an exciting course from a professor, Dr. Schuller from the technical university of darmstadt and head of an institute there. The book on which he builds his course on theoretical mechanical physiscs was build upon diverse kinds of topologies, as Dr. Kevlin says, the Mathematics of "Closeness and Position", the book is called "Gravitation" by "Charles W. Misner, Kip S. Thorne John Archibald Wheeler". I do not remember from where I did download the PDF of this 2 Volume book, for free and legal.
What I did learn by then was that mathematics has undergone a revolutionary development in those nearly 4 decades since I was at the university. Dr. Kevlin expresses this too! So restarting my competence in Mathematics resulted in more than just refreshing my former knowledge from my days at the university. The courses of the Bachelor in Mathematics is really a combination of learning to think as a mathematician as Dr. Kevlin course presents and getting a toolbox of mathematics. Real mathematics in my personal opinion is the key competence to work in todays technology fields. I do regret to have studied mechanical engineering. There I was taught that mathematics is not a competence to understand, but to know to which basic formula styles a problem can be mapped to and the apply the established methodology! I also would have choosen to be 20 years old today and delve into the sciences the way it is done in the 21 st. century and having all those opportunities that MOOC courses open!