It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 21 042 is not a prime number.
For example, 21 042 can be divided by 2: 21 042 / 2 = 10 521.
For 21 042 to be a prime number, it would have been required that 21 042 has only two divisors, i.e., itself and 1.
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21 042 is an even number, because it is evenly divisible by 2: 21 042 / 2 = 10 521.
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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 21 042 is about 145.059.
Thus, the square root of 21 042 is not an integer, and therefore 21 042 is not a square number.
The square of a number (here 21 042) is the result of the product of this number (21 042) by itself (i.e., 21 042 × 21 042); the square of 21 042 is sometimes called "raising 21 042 to the power 2", or "21 042 squared".
The square of 21 042 is 442 765 764 because 21 042 × 21 042 = 21 0422 = 442 765 764.
As a consequence, 21 042 is the square root of 442 765 764.
The multiples of 21 042 are all integers evenly divisible by 21 042, that is all numbers such that the remainder of the division by 21 042 is zero. There are infinitely many multiples of 21 042. The smallest multiples of 21 042 are: