Testing if a Number is Prime

A positive whole number  
  is prime if it is divisible by just two numbers - 1 and itself.
1 is not a prime number.
We can test if a number  
  is prime by dividing by all the whole numbers up to and including  
We need not go so far. In fact we need only divide by the prime numbers up to  
Example: is 77 prime?\[\sqrt{77} =8.7....\]
  so we nee only divide by prime numbers up to and including 8.
. These are 2, 3, 5, 7




\[77=11 \times 7\]
  is nor prime.