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.
All numbers divisible by 5.
All numbers divisible by 5 except 5 that is.
Is 60 a prime number?
So no, 60 is not a prime number because 2 can divide into it.
Is 75 a prime number?
So no, 75 is not a prime number because 5 can divide into it.
Is 31 a prime number?
Could be but you need to check out some more numbers to finally be certain.