Bid for this paper on ebay: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=221156224355 Professor Copeland on Keith numbers, clusters and "reverse Keiths". More links & stuff in full description below ↓↓↓ And before commenting on the merits of "recreational maths" - hear what Ed says. Ed tweets at https://twitter.com/ProfEdCopeland Keith Numbers are also known as repfigit numbers (repetitive Fibonacci-like digit). We also spoke with Mike Keith about his numbers and he issued a playful challenge: "There are many variations on this idea that you can imagine. For example, for a 3-digit number, instead of the next term being a+b+c (a,b,c being the three previous terms) it could be a+2b+3c, or a^2 + b + c or even more fancifully, 2a + b + the cth prime number. You could think up your own version, and name it after yourself!" 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 Numberphile T-Shirts: null Other merchandise: https://store.dftba.com/collections/numberphile