Practical Numbers
Featuring Dr James Grime.
Patreon: http://www.patreon.com/numberphile
Practical Numbers (AKA panarithmic numbers) on the OEIS: https://oeis.org/A005153
James Grime: https://www.singingbanana.com
His YouTube channel: https://www.youtube.com/user/singingbanana
More James on Numberphile: http://bit.ly/grimevideos