understanding that some numbers have special properties and that these properties can be used to solve problems
representing composite numbers as a product of their prime factors and using this form to simplify calculations by cancelling common primes
understanding that if a number is divisible by a composite number then it is also divisible by the prime factors of that number (for example 216 is divisible by 8 because the number represented by the last three digits is divisible by 8, and hence 216 is also divisible by 2 and 4)