Aptitude - Numbers - Discussion

Discussion Forum : Numbers - General Questions (Q.No. 1)
1.
Which one of the following is not a prime number?
31
61
71
91
Answer: Option
Explanation:
91 is divisible by 7. So, it is not a prime number.
Discussion:
112 comments Page 12 of 12.

Kulkarni said:   2 decades ago
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.

Nishant said:   2 decades ago
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?


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