I really don’t know how YouTube measures popularity in its auto-generated lists.
I see that my lecture on “Sets and subsets” is now listed first in the Popular Pure Mathematics Videos there … currently it has 10 views!
This module is now represented twice in the “Popular Pure Mathematics Playlists” because another YouTube user has made a small playlist with some of the videos in, and his version is also apparently very popular, as measured by YouTube.
Meanwhile, the first lecture (well, actually the version from 2012-13, as explained earlier) is actually beginning to pick up hits faster now … so of course it has lost top spot and has moved down the list of popular videos.
Anyway, thanks again to Sally Hanford, the first 12 videos from G11FPM Foundations of Pure Mathematics are now on YouTube Edu and on iTunes U.