Aptitude - Numbers - Discussion
Discussion Forum : Numbers - General Questions (Q.No. 1)
1.
Which one of the following is not a prime number?
Answer: Option
Explanation:
91 is divisible by 7. So, it is not a prime number.
Discussion:
112 comments Page 11 of 12.
Santhosh said:
1 decade ago
How you will consider 7 when you are checking for 31?
Vengala rao said:
2 decades ago
Hai, santhosh your explanation is very nice.
Raji said:
2 decades ago
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
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
Hariharan said:
2 decades ago
Hi, santhosh.
Please explain your formula with an example.
Please explain your formula with an example.
Santosh said:
2 decades ago
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
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
Prasath said:
2 decades ago
n*n>=p plz give any example
Prasath said:
2 decades ago
Please give any one example.
Niki said:
2 decades ago
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
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
Tejas Mehta said:
2 decades ago
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.
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.
Dharmendra said:
2 decades ago
What is the meaning of " k " ? 6k+1 or 6k-1 please explain.
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