It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 21 489 is not a prime number.
For example, 21 489 can be divided by 3: 21 489 / 3 = 7 163.
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For 21 489 to be a prime number, it would have been required that 21 489 has only two divisors, i.e., itself and 1.
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21 489 is an odd number, because it is not evenly divisible by 2.
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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 21 489 is about 146.591.
Thus, the square root of 21 489 is not an integer, and therefore 21 489 is not a square number.
The square of a number (here 21 489) is the result of the product of this number (21 489) by itself (i.e., 21 489 × 21 489); the square of 21 489 is sometimes called "raising 21 489 to the power 2", or "21 489 squared".
The square of 21 489 is 461 777 121 because 21 489 × 21 489 = 21 4892 = 461 777 121.
As a consequence, 21 489 is the square root of 461 777 121.
The multiples of 21 489 are all integers evenly divisible by 21 489, that is all numbers such that the remainder of the division by 21 489 is zero. There are infinitely many multiples of 21 489. The smallest multiples of 21 489 are: