It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 21 742 is not a prime number.
For example, 21 742 can be divided by 2: 21 742 / 2 = 10 871.
For 21 742 to be a prime number, it would have been required that 21 742 has only two divisors, i.e., itself and 1.
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21 742 is an even number, because it is evenly divisible by 2: 21 742 / 2 = 10 871.
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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 21 742 is about 147.452.
Thus, the square root of 21 742 is not an integer, and therefore 21 742 is not a square number.
The square of a number (here 21 742) is the result of the product of this number (21 742) by itself (i.e., 21 742 × 21 742); the square of 21 742 is sometimes called "raising 21 742 to the power 2", or "21 742 squared".
The square of 21 742 is 472 714 564 because 21 742 × 21 742 = 21 7422 = 472 714 564.
As a consequence, 21 742 is the square root of 472 714 564.
The multiples of 21 742 are all integers evenly divisible by 21 742, that is all numbers such that the remainder of the division by 21 742 is zero. There are infinitely many multiples of 21 742. The smallest multiples of 21 742 are: