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:
111 comments Page 12 of 12.

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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