639880921 has 4 divisors (see below), whose sum is σ = 642913744. Its totient is φ = 636848100.

The previous prime is 639880877. The next prime is 639880949. The reversal of 639880921 is 129088936.

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 639880921 - 2¹¹ = 639878873 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (639880981) 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, 1516095 + ... + 1516516.

It is an arithmetic number, because the mean of its divisors is an integer number (160728436).

Almost surely, 2^639880921 is an apocalyptic number.

It is an amenable number.

639880921 is a deficient number, since it is larger than the sum of its proper divisors (3032823).

639880921 is a wasteful number, since it uses less digits than its factorization.

639880921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3032822.

The product of its (nonzero) digits is 186624, while the sum is 46.

The square root of 639880921 is about 25295.8676664786. The cubic root of 639880921 is about 861.7204252125.

The spelling of 639880921 in words is "six hundred thirty-nine million, eight hundred eighty thousand, nine hundred twenty-one".