21-card trick

Additional information

A simple trick with some neat math behind it. More on Numberphile cards at: http://www.bradyharanblog.com/numberphile-playing-cards

More cards video: http://bit.ly/Cards_Shuffling

This video features Anastasia Chavez: http://anastasiachavez.academia.edu/cv

We did a similar video to this about six years ago with Matt Parker (and 27 cards): https://youtu.be/l7lP9y7Bb5g