Modular Arithmetic Courses
University of California, San Diego via Coursera More Fun with Prime Numbers
Kyoto University via edX Mathematical Foundations for Cryptography
University of Colorado System via Coursera Mathematics for Computer Science
University of London International Programmes via Coursera Algorithms with Numbers
Saint Petersburg State University via Coursera Number Theory
Brilliant Introduction to Number Theory
Higher School of Economics via Coursera Number Theory Math for Fun
blackpenredpen via YouTube Number Theory
YouTube