It is possible to find out using mathematical methods whether a given integer is a prime number or not.
No, 138 721 is not a prime number.
For example, 138 721 can be divided by 11: 138 721 / 11 = 12 611.
For 138 721 to be a prime number, it would have been required that 138 721 has only two divisors, i.e., itself and 1.
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138 721 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 138 721 is about 372.453.
Thus, the square root of 138 721 is not an integer, and therefore 138 721 is not a square number.
The square of a number (here 138 721) is the result of the product of this number (138 721) by itself (i.e., 138 721 × 138 721); the square of 138 721 is sometimes called "raising 138 721 to the power 2", or "138 721 squared".
The square of 138 721 is 19 243 515 841 because 138 721 × 138 721 = 138 7212 = 19 243 515 841.
As a consequence, 138 721 is the square root of 19 243 515 841.
The multiples of 138 721 are all integers evenly divisible by 138 721, that is all numbers such that the remainder of the division by 138 721 is zero. There are infinitely many multiples of 138 721. The smallest multiples of 138 721 are: