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The circles with just one colour are prime numbers. The other circles are numbers that are made from those prime numbers. For example three is a prime number and nine will have a line down the middle as it is a multiple of three and not a prime number. The two halves will be colour-coded the same colour as they are representing three, as it is a factor of nine. This works the same as any other number. Twenty-four will have the colours of two, two, two and three. Twelve will have the colours of two, two and three. this is how the system works.