It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 21 008 is not a prime number.
For example, 21 008 can be divided by 2: 21 008 / 2 = 10 504.
For 21 008 to be a prime number, it would have been required that 21 008 has only two divisors, i.e., itself and 1.
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21 008 is an even number, because it is evenly divisible by 2: 21 008 / 2 = 10 504.
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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 21 008 is about 144.941.
Thus, the square root of 21 008 is not an integer, and therefore 21 008 is not a square number.
The square of a number (here 21 008) is the result of the product of this number (21 008) by itself (i.e., 21 008 × 21 008); the square of 21 008 is sometimes called "raising 21 008 to the power 2", or "21 008 squared".
The square of 21 008 is 441 336 064 because 21 008 × 21 008 = 21 0082 = 441 336 064.
As a consequence, 21 008 is the square root of 441 336 064.
The multiples of 21 008 are all integers evenly divisible by 21 008, that is all numbers such that the remainder of the division by 21 008 is zero. There are infinitely many multiples of 21 008. The smallest multiples of 21 008 are: