It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 644 638 is not a prime number.
For example, 644 638 can be divided by 2: 644 638 / 2 = 322 319.
For 644 638 to be a prime number, it would have been required that 644 638 has only two divisors, i.e., itself and 1.
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644 638 is an even number, because it is evenly divisible by 2: 644 638 / 2 = 322 319.
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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 644 638 is about 802.894.
Thus, the square root of 644 638 is not an integer, and therefore 644 638 is not a square number.
The square of a number (here 644 638) is the result of the product of this number (644 638) by itself (i.e., 644 638 × 644 638); the square of 644 638 is sometimes called "raising 644 638 to the power 2", or "644 638 squared".
The square of 644 638 is 415 558 151 044 because 644 638 × 644 638 = 644 6382 = 415 558 151 044.
As a consequence, 644 638 is the square root of 415 558 151 044.
The multiples of 644 638 are all integers evenly divisible by 644 638, that is all numbers such that the remainder of the division by 644 638 is zero. There are infinitely many multiples of 644 638. The smallest multiples of 644 638 are: