Is 491 a prime number?

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

Find out more:

• What is an even 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 491 is about 22.159.

Thus, the square root of 491 is not an integer, and therefore 491 is not a square number.

Anyway, 491 is a prime number, and a prime number cannot be a perfect square.

The square of a number (here 491) is the result of the product of this number (491) by itself (i.e., 491 × 491); the square of 491 is sometimes called "raising 491 to the power 2", or "491 squared".

The square of 491 is 241 081 because 491 × 491 = 491² = 241 081.

As a consequence, 491 is the square root of 241 081.

491 is a number with 3 digits.

The multiples of 491 are all integers evenly divisible by 491, that is all numbers such that the remainder of the division by 491 is zero. There are infinitely many multiples of 491. The smallest multiples of 491 are:

• 0: indeed, 0 is divisible by any natural number, and it is thus a multiple of 491 too, since 0 × 491 = 0
• 491: indeed, 491 is a multiple of itself, since 491 is evenly divisible by 491 (we have 491 / 491 = 1, so the remainder of this division is indeed zero)
• 982: indeed, 982 = 491 × 2
• 1 473: indeed, 1 473 = 491 × 3
• 1 964: indeed, 1 964 = 491 × 4
• 2 455: indeed, 2 455 = 491 × 5
• etc.

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 491). 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 22.159). 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.

• Preceding numbers: …489, 490
• Following numbers: 492, 493…

Nearest numbers from 491

• Preceding prime number: 487
• Following prime number: 499

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• 491 est-il un nombre premier ?