Stage: 2 Challenge Level: 
What are the squares of the numbers from $4$ to $20$?
What happens when you add two prime numbers together?
What happens if you add two different prime numbers together?
Investigations. Visualising. Multiplication & division. Square numbers. Working systematically. Addition & subtraction. Combinations. Trial and improvement. Prime numbers. Factors and multiples.
Published January 2003.
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