Is 639 a prime number?

It is possible to find out using mathematical methods whether a given integer is a prime number or not.

For 639, the answer is: No, 639 is not a prime number.

The list of all positive divisors (i.e., the list of all integers that divide 639) is as follows: 1, 3, 9, 71, 213, 639.

For 639 to be a prime number, it would have been required that 639 has only two divisors, i.e., itself and 1.

Find out more:

What is a prime number?

As a consequence:

639 is a multiple of 1
639 is a multiple of 3
639 is a multiple of 9
639 is a multiple of 71
639 is a multiple of 213

For 639 to be a prime number, it would have been required that 639 has only two divisors, i.e., itself and 1.

Is 639 a deficient number?

Yes, 639 is a deficient number, that is to say 639 is a natural number that is strictly larger than the sum of its proper divisors, i.e., the divisors of 639 without 639 itself (that is 1 + 3 + 9 + 71 + 213 = 297).

Parity of 639

639 is an odd number, because it is not evenly divisible by 2.

Find out more:

What is an even number?

Is 639 a perfect square number?

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 639 is about 25.278.

Thus, the square root of 639 is not an integer, and therefore 639 is not a square number.

What is the square number of 639?

The square of a number (here 639) is the result of the product of this number (639) by itself (i.e., 639 × 639); the square of 639 is sometimes called "raising 639 to the power 2", or "639 squared".

The square of 639 is 408 321 because 639 × 639 = 639² = 408 321.

As a consequence, 639 is the square root of 408 321.

Number of digits of 639

639 is a number with 3 digits.

What are the multiples of 639?

The multiples of 639 are all integers evenly divisible by 639, that is all numbers such that the remainder of the division by 639 is zero. There are infinitely many multiples of 639. The smallest multiples of 639 are:

0: indeed, 0 is divisible by any natural number, and it is thus a multiple of 639 too, since 0 × 639 = 0
639: indeed, 639 is a multiple of itself, since 639 is evenly divisible by 639 (we have 639 / 639 = 1, so the remainder of this division is indeed zero)
1 278: indeed, 1 278 = 639 × 2
1 917: indeed, 1 917 = 639 × 3
2 556: indeed, 2 556 = 639 × 4
3 195: indeed, 3 195 = 639 × 5
etc.

How to determine whether an integer is a prime number?

To determine the primality of a number, several algorithms can be used. The most naive technique is to test all divisors strictly smaller to the number of which we want to determine the primality (here 639). First, we can eliminate all even numbers greater than 2 (and hence 4, 6, 8…). Then, we can stop this check when we reach the square root of the number of which we want to determine the primality (here the square root is about 25.278). Historically, the sieve of Eratosthenes (dating from the Greek mathematics) implements this technique in a relatively efficient manner.

More modern techniques include the sieve of Atkin, probabilistic algorithms, and the cyclotomic AKS test.

Numbers near 639

Preceding numbers: …637, 638
Following numbers: 640, 641…

Nearest numbers from 639

Preceding prime number: 631
Following prime number: 641