Prime Numbers are like phone numbers - there is no real pattern to them and you can easily look them up.  One of Einstein's colleagues asked him for his telephone number one day. Einstein reached for a telephone directory and looked it up. "You don't remember your own number?" the man asked, startled. "No," Einstein answered. "Why should I memorize something I can so easily get from a book?" That said, to quickly complete some transfer test questions, you need to be able to recall the first few prime numbers quickly.

## A prime number can only be divided evenly by itself and one.

Consider the whole number 5 - I have five sweets and want to share them out evenly - I can only give them all to one person or one each to five people. Five is, therefore, prime.

## One is not a prime number

This is a source of much debate for mathematicians but let's just agree that it's not.

## Two is the only even prime number.

The rest of the even numbers can be divided by two so they can't be prime.

## No prime number greater than 5 ends in a 5.

Any number greater than 5 that ends in a 5 can be divided by 5.

Here are the first nineteen primes. Know these and I think that you'll be OK for the transfer test.

## 67

Notice that there is no 1? One is not, we may have mentioned, a prime number.

So how might this come up?

When completing a question like this in the transfer test, encourage your child to cross through the non-primes by thinking of their times tables.

Remember that any multiple of three can quickly be tested by adding together the digits until you get down to a single digit - then if it's 3, 6 or 9 then the original number was a multiple of 3..

ie) 1234 → 1 + 2 + 3 + 4 = 10 → 1+0 = 1. Thus 1234 is not a multiple of 3.

but 1236 → 1 + 2 + 3 + 6 = 12 → 1+2 = 3. Thus 1236 is a multiple of 3.

[hint: the two prime numbers are 31 and 2. The answer is 62]