Is 221 a prime number? What are the divisors of 221?

## Parity of 221

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

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## Is 221 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 221 is about 14.866.

Thus, the square root of 221 is not an integer, and therefore 221 is not a square number.

## What is the square number of 221?

The square of a number (here 221) is the result of the product of this number (221) by itself (i.e., 221 × 221); the square of 221 is sometimes called "raising 221 to the power 2", or "221 squared".

The square of 221 is 48 841 because 221 × 221 = 2212 = 48 841.

As a consequence, 221 is the square root of 48 841.

## Number of digits of 221

221 is a number with 3 digits.

## What are the multiples of 221?

The multiples of 221 are all integers evenly divisible by 221, that is all numbers such that the remainder of the division by 221 is zero. There are infinitely many multiples of 221. The smallest multiples of 221 are:

• 0: indeed, 0 is divisible by any natural number, and it is thus a multiple of 221 too, since 0 × 221 = 0
• 221: indeed, 221 is a multiple of itself, since 221 is evenly divisible by 221 (we have 221 / 221 = 1, so the remainder of this division is indeed zero)
• 442: indeed, 442 = 221 × 2
• 663: indeed, 663 = 221 × 3
• 884: indeed, 884 = 221 × 4
• 1 105: indeed, 1 105 = 221 × 5
• etc.

## 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 221). 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 14.866). 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 221

• Preceding numbers: …219, 220
• Following numbers: 222, 223

### Nearest numbers from 221

• Preceding prime number: 211
• Following prime number: 223
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