639729 has 6 divisors (see below), whose sum is σ = 924066. Its totient is φ = 426480.

The previous prime is 639719. The next prime is 639731. The reversal of 639729 is 927936.

639729 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 608400 + 31329 = 780^2 + 177^2 .

It is not a de Polignac number, because 639729 - 2⁴ = 639713 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 639693 and 639702.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639719) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 35532 + ... + 35549.

It is an arithmetic number, because the mean of its divisors is an integer number (154011).

2⁶³⁹⁷²⁹ is an apocalyptic number.

It is an amenable number.

639729 is a deficient number, since it is larger than the sum of its proper divisors (284337).

639729 is a wasteful number, since it uses less digits than its factorization.

639729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 71087 (or 71084 counting only the distinct ones).

The product of its digits is 20412, while the sum is 36.

The square root of 639729 is about 799.8306070663. The cubic root of 639729 is about 86.1652223048.

The spelling of 639729 in words is "six hundred thirty-nine thousand, seven hundred twenty-nine".