Is 861 a prime number? What are the divisors of 861?

## Parity of 861

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

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## Is 861 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 861 is about 29.343.

Thus, the square root of 861 is not an integer, and therefore 861 is not a square number.

## What is the square number of 861?

The square of a number (here 861) is the result of the product of this number (861) by itself (i.e., 861 × 861); the square of 861 is sometimes called "raising 861 to the power 2", or "861 squared".

The square of 861 is 741 321 because 861 × 861 = 8612 = 741 321.

As a consequence, 861 is the square root of 741 321.

## Number of digits of 861

861 is a number with 3 digits.

## What are the multiples of 861?

The multiples of 861 are all integers evenly divisible by 861, that is all numbers such that the remainder of the division by 861 is zero. There are infinitely many multiples of 861. The smallest multiples of 861 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 861). 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 29.343). 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 861

• Preceding numbers: …859, 860
• Following numbers: 862, 863

### Nearest numbers from 861

• Preceding prime number: 859
• Following prime number: 863
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