It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 21 007 is not a prime number.
For example, 21 007 can be divided by 7: 21 007 / 7 = 3 001.
For 21 007 to be a prime number, it would have been required that 21 007 has only two divisors, i.e., itself and 1.
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21 007 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 21 007 is about 144.938.
Thus, the square root of 21 007 is not an integer, and therefore 21 007 is not a square number.
The square of a number (here 21 007) is the result of the product of this number (21 007) by itself (i.e., 21 007 × 21 007); the square of 21 007 is sometimes called "raising 21 007 to the power 2", or "21 007 squared".
The square of 21 007 is 441 294 049 because 21 007 × 21 007 = 21 0072 = 441 294 049.
As a consequence, 21 007 is the square root of 441 294 049.
The multiples of 21 007 are all integers evenly divisible by 21 007, that is all numbers such that the remainder of the division by 21 007 is zero. There are infinitely many multiples of 21 007. The smallest multiples of 21 007 are: