Is 21991 a prime number?

21 991 is an odd number, because it is not evenly divisible by 2.

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• 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 21 991 is about 148.294.

Thus, the square root of 21 991 is not an integer, and therefore 21 991 is not a square number.

Anyway, 21 991 is a prime number, and a prime number cannot be a perfect square.

The square of a number (here 21 991) is the result of the product of this number (21 991) by itself (i.e., 21 991 × 21 991); the square of 21 991 is sometimes called "raising 21 991 to the power 2", or "21 991 squared".

The square of 21 991 is 483 604 081 because 21 991 × 21 991 = 21 991² = 483 604 081.

As a consequence, 21 991 is the square root of 483 604 081.

21 991 is a number with 5 digits.

The multiples of 21 991 are all integers evenly divisible by 21 991, that is all numbers such that the remainder of the division by 21 991 is zero. There are infinitely many multiples of 21 991. The smallest multiples of 21 991 are:

• 0: indeed, 0 is divisible by any natural number, and it is thus a multiple of 21 991 too, since 0 × 21 991 = 0
• 21 991: indeed, 21 991 is a multiple of itself, since 21 991 is evenly divisible by 21 991 (we have 21 991 / 21 991 = 1, so the remainder of this division is indeed zero)
• 43 982: indeed, 43 982 = 21 991 × 2
• 65 973: indeed, 65 973 = 21 991 × 3
• 87 964: indeed, 87 964 = 21 991 × 4
• 109 955: indeed, 109 955 = 21 991 × 5
• etc.

• Preceding numbers: …21 989, 21 990
• Following numbers: 21 992, 21 993…

Nearest numbers from 21 991

• Preceding prime number: 21 977
• Following prime number: 21 997

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• 21 991 est-il un nombre premier ?