Discussing vertex covers and Alcuin numbers for graphs - and a famous old puzzle. Filmed at MSRI with Dr Annie Raymond. More links & stuff in full description below ↓↓↓ Annie Raymond: https://www.msri.org/people/38568 The Alcuin Number of a Graph: https://link.springer.com/chapter/10.1007/978-3-540-87744-8_27 Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile We are also supported by Science Sandbox, a Simons Foundation initiative dedicated to engaging everyone with the process of science. Discuss this video on Brady's subreddit: https://redd.it/7ob1n2 NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Subscribe: http://bit.ly/Numberphile_Sub Videos by Brady Haran Patreon: http://www.patreon.com/numberphile Brady's videos subreddit: http://www.reddit.com/r/BradyHaran/ Brady's latest videos across all channels: http://www.bradyharanblog.com/ Sign up for (occasional) emails: http://eepurl.com/YdjL9