Is 991 a prime number? What are the divisors of 991?

## Parity of 991

991 is an odd number, because it is not evenly divisible by 2.

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## Is 991 a perfect square number?

A number is a perfect square (or a square number) if its square root is an integer; that is to say, it is the product of an integer with itself. Here, the square root of 991 is about 31.480.

Thus, the square root of 991 is not an integer, and therefore 991 is not a square number.

Anyway, 991 is a prime number, and a prime number cannot be a perfect square.

## What is the square number of 991?

The square of a number (here 991) is the result of the product of this number (991) by itself (i.e., 991 × 991); the square of 991 is sometimes called "raising 991 to the power 2", or "991 squared".

The square of 991 is 982 081 because 991 × 991 = 9912 = 982 081.

As a consequence, 991 is the square root of 982 081.

## Number of digits of 991

991 is a number with 3 digits.

## What are the multiples of 991?

The multiples of 991 are all integers evenly divisible by 991, that is all numbers such that the remainder of the division by 991 is zero. There are infinitely many multiples of 991. The smallest multiples of 991 are:

## How to determine whether an integer is a prime number?

To determine the primality of a number, several algorithms can be used. The most naive technique is to test all divisors strictly smaller to the number of which we want to determine the primality (here 991). First, we can eliminate all even numbers greater than 2 (and hence 4, 6, 8…). Then, we can stop this check when we reach the square root of the number of which we want to determine the primality (here the square root is about 31.480). Historically, the sieve of Eratosthenes (dating from the Greek mathematics) implements this technique in a relatively efficient manner.

More modern techniques include the sieve of Atkin, probabilistic algorithms, and the cyclotomic AKS test.

## Numbers near 991

• Preceding numbers: …989, 990
• Following numbers: 992, 993

### Nearest numbers from 991

• Preceding prime number: 983
• Following prime number: 997
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