Prime numbers at a glance

If you have a number and want to know could it be a prime number remember (a sort of quick first check)

All even numbers are NOT prime numbers.

All even numbers except 2 that is.

And

All numbers divisible by 5.

All numbers divisible by 5 except 5 that is.

Example 1

Is 60 a prime number?

$60/2=30$

So no, 60 is not a prime number because 2 can divide into it.

Example 2

Is 75 a prime number?

$75/2=37.5$ $75/5=15$

So no, 75 is not a prime number because 5 can divide into it.

Example 3

Is 31 a prime number?

$31/2=15.5$ $31/5=6.2$

Could be but you need to check out some more numbers to finally be certain.