6639 has 4 divisors (see below), whose sum is σ = 8856. Its totient is φ = 4424.

The previous prime is 6637. The next prime is 6653. The reversal of 6639 is 9366.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 6639 - 2¹ = 6637 is a prime.

It is a D-number.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6637) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1104 + ... + 1109.

It is an arithmetic number, because the mean of its divisors is an integer number (2214).

2⁶⁶³⁹ is an apocalyptic number.

6639 is a deficient number, since it is larger than the sum of its proper divisors (2217).

6639 is a wasteful number, since it uses less digits than its factorization.

6639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2216.

The product of its digits is 972, while the sum is 24.

The square root of 6639 is about 81.4800589101. The cubic root of 6639 is about 18.7946491487.

It can be divided in two parts, 66 and 39, that added together give a triangular number (105 = T₁₄).

The spelling of 6639 in words is "six thousand, six hundred thirty-nine".