639662721 has 16 divisors (see below), whose sum is σ = 898310400. Its totient is φ = 403755408.

The previous prime is 639662713. The next prime is 639662731. The reversal of 639662721 is 127266936.

It is not a de Polignac number, because 639662721 - 2³ = 639662713 is a prime.

It is not an unprimeable number, because it can be changed into a prime (639662731) 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 15 ways as a sum of consecutive naturals, for example, 172990 + ... + 176648.

It is an arithmetic number, because the mean of its divisors is an integer number (56144400).

Almost surely, 2^639662721 is an apocalyptic number.

It is an amenable number.

639662721 is a deficient number, since it is larger than the sum of its proper divisors (258647679).

639662721 is a wasteful number, since it uses less digits than its factorization.

639662721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6748.

The product of its digits is 163296, while the sum is 42.

The square root of 639662721 is about 25291.5543413211. The cubic root of 639662721 is about 861.6224649165.

The spelling of 639662721 in words is "six hundred thirty-nine million, six hundred sixty-two thousand, seven hundred twenty-one".