Stage: 2 and 3 Challenge Level: 
Divisibility. Generalising. Games. Visualising. Mathematical reasoning & proof. Working systematically. Creating expressions/formulae. Interactivities. Addition & subtraction. Factors and multiples.
Published January 2002,February 2009.
Copyright © 2007. University of Cambridge. All rights reserved.
NRICH is part of the family of activities in the Millennium Mathematics Project, which also includes the Plus and Motivate sites.
email: nrich@damtp.cam.ac.uk
