It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 990 991 is not a prime number.
For example, 990 991 can be divided by 443: 990 991 / 443 = 2 237.
For 990 991 to be a prime number, it would have been required that 990 991 has only two divisors, i.e., itself and 1.
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990 991 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 990 991 is about 995.485.
Thus, the square root of 990 991 is not an integer, and therefore 990 991 is not a square number.
The square of a number (here 990 991) is the result of the product of this number (990 991) by itself (i.e., 990 991 × 990 991); the square of 990 991 is sometimes called "raising 990 991 to the power 2", or "990 991 squared".
The square of 990 991 is 982 063 162 081 because 990 991 × 990 991 = 990 9912 = 982 063 162 081.
As a consequence, 990 991 is the square root of 982 063 162 081.
The multiples of 990 991 are all integers evenly divisible by 990 991, that is all numbers such that the remainder of the division by 990 991 is zero. There are infinitely many multiples of 990 991. The smallest multiples of 990 991 are: