It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 9 991 is not a prime number.
For example, 9 991 can be divided by 97: 9 991 / 97 = 103.
For 9 991 to be a prime number, it would have been required that 9 991 has only two divisors, i.e., itself and 1.
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9 991 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 9 991 is about 99.955.
Thus, the square root of 9 991 is not an integer, and therefore 9 991 is not a square number.
The square of a number (here 9 991) is the result of the product of this number (9 991) by itself (i.e., 9 991 × 9 991); the square of 9 991 is sometimes called "raising 9 991 to the power 2", or "9 991 squared".
The square of 9 991 is 99 820 081 because 9 991 × 9 991 = 9 9912 = 99 820 081.
As a consequence, 9 991 is the square root of 99 820 081.
The multiples of 9 991 are all integers evenly divisible by 9 991, that is all numbers such that the remainder of the division by 9 991 is zero. There are infinitely many multiples of 9 991. The smallest multiples of 9 991 are: