a factor is a number that divides into another number exactly, with no remainder

the largest factor of any number is the number itself

no number has any factors greater than the number itself

to find all the factors of a number, write all the pairs of numbers that multiply to give the original number

**common factor**

a common factor is one that appears in the factor lists of 2 or more given numbers.

1 is the first factor of every number

**highest common factor**

the highest common factor or HCF is the largest of the common factors

**perfect number**

a perfect number is a number for which the sum of its factors (excluding the number itself) equals the number.

the first perfect number is 6, as 1+ 2 + 3 = 6

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