What I saw on the web on 2024.11.21

1. I cracked the divisibility code.
   by Matt Parker
   https://www.youtube.com/watch?v=6pLz8wEQYkA
   as per the comments, i'm fond of the 1001 divisbility test, which tests 7, 11, and 13 at the same time, and essentially lets you play with your number in blocks of 3 digits
   via rss