639891 has 18 divisors (see below), whose sum is σ = 1075932. Its totient is φ = 365400.

The previous prime is 639857. The next prime is 639907. The reversal of 639891 is 198936.

639891 is nontrivially palindromic in base 5.

639891 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 639891 - 2¹⁹ = 115603 is a prime.

It is not an unprimeable number, because it can be changed into a prime (639851) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 285 + ... + 1166.

It is an arithmetic number, because the mean of its divisors is an integer number (59774).

2⁶³⁹⁸⁹¹ is an apocalyptic number.

639891 is a deficient number, since it is larger than the sum of its proper divisors (436041).

639891 is a wasteful number, since it uses less digits than its factorization.

639891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1471 (or 1461 counting only the distinct ones).

The product of its digits is 11664, while the sum is 36.

The square root of 639891 is about 799.9318720991. The cubic root of 639891 is about 86.1724949614.

The spelling of 639891 in words is "six hundred thirty-nine thousand, eight hundred ninety-one".