1. Odd numbers1, 3, 5, 7, 9, 11, 13,... Even numbers2, 4, 6, 8, 10, 12, 14,... MultiplesThe multiples of 2 are 2, 4, 6, 8, 10, … The multiples of 3 are 3, 6, 9, 12, 15, … The multiples of 5 are 5, 10, 15, 20, The multiples of 12 are 12, 24, 36, 48, Common Multiples When we look at the multiples of 3 and the multiples of 5 we find that 15 and 30 appear on both lists. They are called common multiples. Lowest common multiple 15 is the smallest multiple of both 3 and 5. It is called the lowest common multiple.

2. Factors A number which divides exactly into another number is called a factor. Factors are whole numbers and they come in pairs. Eg Find the factors of 24 24 = 1 x 24 or 24 = 2 x 12 or 24 = 3 x 8 or 24 = 4 x 6 The factors of 24 are 1, 2, 3, 4, 6, 12 and 24 Prime numbersPrime numbers have only two factors, themselves and 1. The first few prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29,...

3. Prime factors The factors of 24 are 1, 2, 3, 4, 6, 12 and 24 2 and 3 are also prime numbers. 2 and 3 are called prime factors of 24. Square numbers The square numbers are 1, 4, 9, 16,... Triangle numbers The triangle numbers are 1, 3, 6, 10,...