It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 642 638 is not a prime number.
For example, 642 638 can be divided by 2: 642 638 / 2 = 321 319.
For 642 638 to be a prime number, it would have been required that 642 638 has only two divisors, i.e., itself and 1.
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642 638 is an even number, because it is evenly divisible by 2: 642 638 / 2 = 321 319.
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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 642 638 is about 801.647.
Thus, the square root of 642 638 is not an integer, and therefore 642 638 is not a square number.
The square of a number (here 642 638) is the result of the product of this number (642 638) by itself (i.e., 642 638 × 642 638); the square of 642 638 is sometimes called "raising 642 638 to the power 2", or "642 638 squared".
The square of 642 638 is 412 983 599 044 because 642 638 × 642 638 = 642 6382 = 412 983 599 044.
As a consequence, 642 638 is the square root of 412 983 599 044.
The multiples of 642 638 are all integers evenly divisible by 642 638, that is all numbers such that the remainder of the division by 642 638 is zero. There are infinitely many multiples of 642 638. The smallest multiples of 642 638 are: