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Today we are going to use Erastothene’s Sieve to find the prime numbers up to 100. You will use the “Count By” app on the iPods or iPads or your netbook with the interactive 100 chart program. Color in the corresponding numbers on your paper 100 chart.

Prime numbers are numbers with exactly two factors – you can divide a prime number by one or itself, but no other number, to get a whole number. The number one only has one factor, so it is not a prime number. So, 2 and 3 are the first two prime numbers. 4 is not a prime number because it has three factors (1, 2 and 4). Circle the prime numbers on your paper chart and stick it firmly in your work book to refer to later.