Stage: 5 Challenge Level: 
Generalising. Inequality/inequalities. Interactivities. Manipulating algebraic expressions/formulae. Practical Activity. Visualising. Mathematical reasoning & proof. Logo. Dynamical systems. Arithmetic sequence. Number theory.
Published December 2001,January 2002.
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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
