7 and Happy Numbers

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...

7 is an example of a happy number, as opposed to sad numbers. What makes a number happy?

Dr Ria Symonds is from the University of Nottingham.

About the brown paper: http://periodicvideos.blogspot.com/2012/02/brown-paper-question.html