639809281 has 4 divisors (see below), whose sum is σ = 661871700. Its totient is φ = 617746864.

The previous prime is 639809273. The next prime is 639809293. The reversal of 639809281 is 182908936.

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

It can be written as a sum of positive squares in 2 ways, for example, as 265038400 + 374770881 = 16280^2 + 19359^2 .

It is not a de Polignac number, because 639809281 - 2³ = 639809273 is a prime.

It is a super-2 number, since 2×639809281² = 818711832107473922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (639809201) 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, 11031166 + ... + 11031223.

It is an arithmetic number, because the mean of its divisors is an integer number (165467925).

Almost surely, 2^639809281 is an apocalyptic number.

It is an amenable number.

639809281 is a deficient number, since it is larger than the sum of its proper divisors (22062419).

639809281 is a wasteful number, since it uses less digits than its factorization.

639809281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22062418.

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

The square root of 639809281 is about 25294.4515852785. The cubic root of 639809281 is about 861.6882650854.

The spelling of 639809281 in words is "six hundred thirty-nine million, eight hundred nine thousand, two hundred eighty-one".