It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 645 509 is not a prime number.
For example, 645 509 can be divided by 79: 645 509 / 79 = 8 171.
For 645 509 to be a prime number, it would have been required that 645 509 has only two divisors, i.e., itself and 1.
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645 509 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 645 509 is about 803.436.
Thus, the square root of 645 509 is not an integer, and therefore 645 509 is not a square number.
The square of a number (here 645 509) is the result of the product of this number (645 509) by itself (i.e., 645 509 × 645 509); the square of 645 509 is sometimes called "raising 645 509 to the power 2", or "645 509 squared".
The square of 645 509 is 416 681 869 081 because 645 509 × 645 509 = 645 5092 = 416 681 869 081.
As a consequence, 645 509 is the square root of 416 681 869 081.
The multiples of 645 509 are all integers evenly divisible by 645 509, that is all numbers such that the remainder of the division by 645 509 is zero. There are infinitely many multiples of 645 509. The smallest multiples of 645 509 are: