# Aptitude - Numbers - Discussion

Discussion Forum : Numbers - General Questions (Q.No. 91)
91.
Which one of the following is a prime number ?
161
221
373
437
None of these
Explanation:

437 > 22

All prime numbers less than 22 are : 2, 3, 5, 7, 11, 13, 17, 19.

161 is divisible by 7, and 221 is divisible by 13.

373 is not divisible by any of the above prime numbers.

373 is prime.

Discussion:
9 comments Page 1 of 1.

Ali said:   8 months ago
What is the connection of square root with a prime number? please explain.

Barsha said:   1 year ago

Radhika Deshmukh said:   4 years ago
161 also divisible by 7.

Ashish said:   6 years ago
161 satisfies 6k-1 (for k = 27) but it is not a prime number why?

Aparna said:   8 years ago
I did not get it please explain me.

Shashank said:   8 years ago
Let p be a given number and n be the smallest counting no such that n^2>p.

Now test whether p is divisible by any of the prime no. less then or equal to n. If yes p is not prime no. otherwise, it is prime.

For ex. 91.

10^>91 and prime no. below 10 are 2, 3, 5, 7 then 91 is divisible by 7.

So 91 is not prime no.

Ashraful said:   8 years ago
As square-root-of(437)is very close to 22 & there is no prime numbers between 20-22 so 437 must be divisible by greater than 22, that must be a prime numbers.

23 is divisor of 437.