639031681 has 4 divisors (see below), whose sum is σ = 639120132. Its totient is φ = 638943232.

The previous prime is 639031663. The next prime is 639031697. The reversal of 639031681 is 186130936.

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 314707600 + 324324081 = 17740^2 + 18009^2 .

It is a cyclic number.

It is not a de Polignac number, because 639031681 - 2¹⁷ = 638900609 is a prime.

It is a super-2 number, since 2×639031681² = 816722978643371522, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 639031681.

It is not an unprimeable number, because it can be changed into a prime (639031621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 32320 + ... + 48193.

It is an arithmetic number, because the mean of its divisors is an integer number (159780033).

Almost surely, 2^639031681 is an apocalyptic number.

It is an amenable number.

639031681 is a deficient number, since it is larger than the sum of its proper divisors (88451).

639031681 is an equidigital number, since it uses as much as digits as its factorization.

639031681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 88450.

The product of its (nonzero) digits is 23328, while the sum is 37.

The square root of 639031681 is about 25279.0759522574. The cubic root of 639031681 is about 861.3390357921.

The spelling of 639031681 in words is "six hundred thirty-nine million, thirty-one thousand, six hundred eighty-one".