all prime numbers above 3 are of the form 6n-1or 6n+1, because all other numbers are divisible by 2 or 3.
Please make clear the meaning of the sentence with example.
Any prime number p>3
when divided by 6 can only give remainder of 1 or 5 (remainder can not be 2 or 4 as in this case p
would be even and remainder can not be 3 as in this case p
would be divisible by 3).
So any prime number p>3
could be expressed as p=6n+1
), where n is an integer >0.
For example: 5=prime=6-1, 7=prime=6+1, 11=prime=6*2-1, 13=prime=6*2+1, 17=prime=6*3-1, ...But:Not all number which yield a remainder of 1 or 5 upon division by 6 are prime
, so vise-versa of above property is not correct. For example 25 yields a remainder of 1 upon division be 6 and it's not a prime number.