639901 has 4 divisors (see below), whose sum is σ = 673600. Its totient is φ = 606204.

The previous prime is 639857. The next prime is 639907. The reversal of 639901 is 109936.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 639901 - 2¹⁹ = 115613 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 639901.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639907) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16821 + ... + 16858.

It is an arithmetic number, because the mean of its divisors is an integer number (168400).

2⁶³⁹⁹⁰¹ is an apocalyptic number.

It is an amenable number.

639901 is a deficient number, since it is larger than the sum of its proper divisors (33699).

639901 is a wasteful number, since it uses less digits than its factorization.

639901 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33698.

The product of its (nonzero) digits is 1458, while the sum is 28.

The square root of 639901 is about 799.9381226070. The cubic root of 639901 is about 86.1729438506.

It can be divided in two parts, 639 and 901, that added together give a triangular number (1540 = T₅₅).

The spelling of 639901 in words is "six hundred thirty-nine thousand, nine hundred one".