639679805 has 4 divisors (see below), whose sum is σ = 767615772. Its totient is φ = 511743840.

The previous prime is 639679787. The next prime is 639679813. The reversal of 639679805 is 508976936.

639679805 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 435389956 + 204289849 = 20866^2 + 14293^2 .

It is not a de Polignac number, because 639679805 - 2⁸ = 639679549 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 63967976 + ... + 63967985.

It is an arithmetic number, because the mean of its divisors is an integer number (191903943).

Almost surely, 2^639679805 is an apocalyptic number.

It is an amenable number.

639679805 is a deficient number, since it is larger than the sum of its proper divisors (127935967).

639679805 is a wasteful number, since it uses less digits than its factorization.

639679805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 127935966.

The product of its (nonzero) digits is 2449440, while the sum is 53.

The square root of 639679805 is about 25291.8920802695. The cubic root of 639679805 is about 861.6301355355.

The spelling of 639679805 in words is "six hundred thirty-nine million, six hundred seventy-nine thousand, eight hundred five".