an excerpt from _the curious incident of the dog in the nighttime_

this is how you know what prime numbers are.

first you write down all the positive whole numbers in the world.

then you take away all the numbers that are multiples of 2. then you take away all the numbers that are multiples of 3. then you take away all the numbers that are multiples of 4 and 5 and 6 and 7 and so on. the numbers that are left are the prime numbers.

the rule for working out prime numbers is really simple, but no one has ever worked out a simple formula for telling you whether a very big number is a prime number or what the next one will be. If a number is really, really big, it can take a computer years to work out whether it is a prime number.

prime numbers are useful for writing codes and in america they are classed as military material and if you find one over 100 digits long you have to tell the cia and they buy it off you for $10,000. But it would not be a very good way of making a living.

prime numbers are what is left when you have taken all the patterns away. i think prime numbers are like life. they are very logical but you could never work out the rules, even if you spent all your time thinking about them.

(p 11-12)