It was a famous problem for many years - until a physics genius solved it all the way to infinity. Featuring author Alex Bellos - more links below. Extras from this interview: https://www.youtube.com/watch?v=jv8dITbiheQ More Numberphile videos with Alex: http://bit.ly/Bellos_Playlist Alex's recent book about puzzles (including the Four 4s): http://amzn.to/2jRo0n2 More Alex books: http://bit.ly/BellosBooks With a sincere thanks to these Patrons... Jeff Straathof Today I Found Out Peggy You'll Christian Cooper Dr Jubal John James Bissonette Ken Baron Andrzej 'Yester' Fiedukowicz Bill Shillito Tony Fadell Erik Alexander Nordlund Thomas Buckingham Susan Silver OK Merli Tyler O'Connor Jon Padden Ciprian Stan Vali Dobrota D Hills Charles Southerland Arnas plusunim Paul Bates Jordan Smith Tracy Parry Kristian Joensen Tryggve Johannesson Alfred Wallace Join out Patreon supporters at: http://www.patreon.com/numberphile 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. 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 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