It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 721 421 is not a prime number.
For example, 721 421 can be divided by 757: 721 421 / 757 = 953.
For 721 421 to be a prime number, it would have been required that 721 421 has only two divisors, i.e., itself and 1.
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721 421 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 721 421 is about 849.365.
Thus, the square root of 721 421 is not an integer, and therefore 721 421 is not a square number.
The square of a number (here 721 421) is the result of the product of this number (721 421) by itself (i.e., 721 421 × 721 421); the square of 721 421 is sometimes called "raising 721 421 to the power 2", or "721 421 squared".
The square of 721 421 is 520 448 259 241 because 721 421 × 721 421 = 721 4212 = 520 448 259 241.
As a consequence, 721 421 is the square root of 520 448 259 241.
The multiples of 721 421 are all integers evenly divisible by 721 421, that is all numbers such that the remainder of the division by 721 421 is zero. There are infinitely many multiples of 721 421. The smallest multiples of 721 421 are: