29 and Leap Years

Alex Bellos discusses how the Incans used knots in string (Quipu) to record numbers.Check out Brilliant (get 20% off their premium service): https://brillian...

Astronomer Dr Meghan Gray on leap years and Julian dates.

Meghan is making a "guest appearance" on Numberphile and is more familiar to viewers of our sister channels DeepSkyVideos and Sixty Symbols.

DeepSkyVideos: https://www.youtube.com/user/deepskyvideos
Sixty Symbols: https://www.youtube.com/user/sixtysymbols