639021 has 8 divisors (see below), whose sum is σ = 868320. Its totient is φ = 417872.

The previous prime is 639011. The next prime is 639043. The reversal of 639021 is 120936.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 639021 - 2⁷ = 638893 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639011) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1851 + ... + 2168.

It is an arithmetic number, because the mean of its divisors is an integer number (108540).

2⁶³⁹⁰²¹ is an apocalyptic number.

It is an amenable number.

639021 is a deficient number, since it is larger than the sum of its proper divisors (229299).

639021 is a wasteful number, since it uses less digits than its factorization.

639021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4075.

The product of its (nonzero) digits is 324, while the sum is 21.

The square root of 639021 is about 799.3878908265. The cubic root of 639021 is about 86.1334236858.

Adding to 639021 its reverse (120936), we get a palindrome (759957).

It can be divided in two parts, 63902 and 1, that added together give a triangular number (63903 = T₃₅₇).

The spelling of 639021 in words is "six hundred thirty-nine thousand, twenty-one".