numbers just indicate the relative level of the course (for example 100 level is generally freshman course, 400 level senior level course, and 500+ grad school level) but after the level, the rest of the numerical designation doesn't really mean much (other than those 101 courses, which are meant to be like the big intro courses). Course number is just a way for departments to organize their curriculum (at least in my school). For example, in my major, students are required to take a certain number of 200+ level course, and a certain number of 450+ level courses. Departments in my school also tend to group a sequence of courses in numerical continuity (for example, freshman engineering math is 191 and 192, and sophomore is 293, 294) a course that's designated 250 isn't necessary harder than a course designated 220.