It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 398 409 is not a prime number.
For example, 398 409 can be divided by 3: 398 409 / 3 = 132 803.
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For 398 409 to be a prime number, it would have been required that 398 409 has only two divisors, i.e., itself and 1.
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398 409 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 398 409 is about 631.196.
Thus, the square root of 398 409 is not an integer, and therefore 398 409 is not a square number.
The square of a number (here 398 409) is the result of the product of this number (398 409) by itself (i.e., 398 409 × 398 409); the square of 398 409 is sometimes called "raising 398 409 to the power 2", or "398 409 squared".
The square of 398 409 is 158 729 731 281 because 398 409 × 398 409 = 398 4092 = 158 729 731 281.
As a consequence, 398 409 is the square root of 158 729 731 281.
The multiples of 398 409 are all integers evenly divisible by 398 409, that is all numbers such that the remainder of the division by 398 409 is zero. There are infinitely many multiples of 398 409. The smallest multiples of 398 409 are: