Ben Sparks discusses aliquot sequences and why 276 holds a surprise. This video continues at and delves into so-called Untouchable Numbers. More links & stuff in full description below ↓↓↓ Ben Sparks: More Ben Sparks on Numberphile: Perfect Numbers on Numberphile: Amicable Numbers: GeoGebra file: Patreon: Numberphile is supported by Jane Street. Learn more about them (and exciting career opportunities) at: We're also supported by the Simons Laufer Mathematical Sciences Institute (formerly MSRI): Our thanks also to the Simons Foundation: NUMBERPHILE Website: Numberphile on Facebook: Numberphile tweets: Subscribe: Videos by Brady Haran Animation by Pete McPartlan Numberphile T-Shirts and Merch: Brady's videos subreddit: Brady's latest videos across all channels: Sign up for (occasional) emails: