It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 688 991 is not a prime number.
For example, 688 991 can be divided by 97: 688 991 / 97 = 7 103.
For 688 991 to be a prime number, it would have been required that 688 991 has only two divisors, i.e., itself and 1.
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688 991 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 688 991 is about 830.055.
Thus, the square root of 688 991 is not an integer, and therefore 688 991 is not a square number.
The square of a number (here 688 991) is the result of the product of this number (688 991) by itself (i.e., 688 991 × 688 991); the square of 688 991 is sometimes called "raising 688 991 to the power 2", or "688 991 squared".
The square of 688 991 is 474 708 598 081 because 688 991 × 688 991 = 688 9912 = 474 708 598 081.
As a consequence, 688 991 is the square root of 474 708 598 081.
The multiples of 688 991 are all integers evenly divisible by 688 991, that is all numbers such that the remainder of the division by 688 991 is zero. There are infinitely many multiples of 688 991. The smallest multiples of 688 991 are: