I know that prime numbers are of the form either 6k-1 or 6K+1 . Here 91 is of the form 6k+1 but still it is prime how come?
Kulkarni said:
(Wed, Sep 22, 2010 02:06:56 PM)
Here we have to notice that the above mentioned is not the general form of a prime number. There is no general form for prime no's, the above mentioned 6k+1 or 6k-1 will help you to find the prime no's but not for all the values of k.
Dharmendra said:
(Tue, Nov 9, 2010 08:11:56 AM)
What is the meaning of " k " ? 6k+1 or 6k-1 please explain.
Tejas Mehta said:
(Mon, Nov 29, 2010 08:04:05 AM)
6k + 1 or 6k - 1 is a simplified form. Any prime number always satisfies this condition,where k can be 1,2,3...9.
But plz Note: Every prime no can be written in the form of 6k+1,6K-1 But every no which can be written in the form of 6k+1,6k-1 are not necessarily prime.
Here 91 can be written as 6k + 1 = 6(15) + 1 where k = 15,
But it is not prime as it is divisible by 13,7.
Niki said:
(Thu, Jan 13, 2011 10:12:56 AM)
We can find whether a given number is prime by using the formula n*n>=p
where n is the smallest number whose square is greater then or equal to p i:e the given number.
if p is divisible by any of the prime numbers less than n then it is not a prime otherwise it is a prime number
Prasath said:
(Thu, Jan 27, 2011 07:13:30 AM)
Please give any one example.
Prasath said:
(Thu, Jan 27, 2011 07:14:53 AM)
n*n>=p plz give any example
Santosh said:
(Sat, Mar 12, 2011 03:55:34 PM)
Hiii friends .......just apply this formula to find the not prime no or prime no...
n*n>=p
1)here P is the given no
2)find the squares which is > or = to the given no P
3)find the prime nos < or = n
4)check weather the given P no is divisible by prime nos which is < or =n
5)if divisible ....it mean it have more than two factors so given P is not a prime no.
6)if not divisible it mean the given no P is prime no
Hariharan said:
(Thu, Mar 24, 2011 03:07:45 AM)
Hi, santhosh.
Please explain your formula with an example.
Raji said:
(Mon, Apr 25, 2011 03:46:35 AM)
Hi, i would like to share with a example
to find 31 prime or not
by the above formula it can be written as 6*6>=31(p)
now upto 6 the prime nos are 2,3,5,7
31 is not divisble by any of these no,
hence it would be a prime no
Vengala Rao said:
(Fri, Jul 1, 2011 05:59:22 AM)
Hai, santhosh your explanation is very nice.
Santhosh said:
(Wed, Aug 10, 2011 11:49:08 AM)
How you will consider 7 when you are checking for 31?
Karthick said:
(Thu, Sep 22, 2011 06:11:31 PM)
Thank you santhose:) your idea is too good to identify the prime no.
