Pre-requisite knowledge before diving into algorithms
To learn algorithms mathematically you will need to have a basic understanding of 


Proofs(basically using induction)
summations and
asymptotic notations(like Big-O , Big-Omega)


To learn the above subjects I recommend this course from  https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-042j-mathematics-for-computer-science-spring-2015/