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A1. Integers
Prime numbers

Vocabulary Because 3 divides into 12 exactly, 3 is called a factor, or divisor, of 12. We also describe 12 as a multiple of 3. Other factors of twelve are 1, 2, 4, 6 and 12. The factors of 18 are 1, 2, 3, 6, 9 and 18. The factors of 16 are 1, 2, 4, 8 and 16. The factors of 35 are 1, 5, 7 and 35. The number 3 has only two factors, 1 and 3. Numbers with exactly two factors are called prime numbers. Other prime numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23 ... 1 is not a prime number as it only has one factor, itself. Enter a number:

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