639657 has 20 divisors (see below), whose sum is σ = 980100. Its totient is φ = 415584.

The previous prime is 639647. The next prime is 639671. The reversal of 639657 is 756936.

It is a happy number.

639657 is digitally balanced in base 7, 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 2 ways, for example, as 254016 + 385641 = 504^2 + 621^2 .

It is not a de Polignac number, because 639657 - 2¹⁰ = 638633 is a prime.

It is a super-2 number, since 2×639657² = 818322155298, which contains 22 as substring.

639657 is strictly pandigital in base 7.

It is not an unprimeable number, because it can be changed into a prime (639637) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 4219 + ... + 4367.

It is an arithmetic number, because the mean of its divisors is an integer number (49005).

2⁶³⁹⁶⁵⁷ is an apocalyptic number.

It is an amenable number.

639657 is a deficient number, since it is larger than the sum of its proper divisors (340443).

639657 is a wasteful number, since it uses less digits than its factorization.

639657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 214 (or 205 counting only the distinct ones).

The product of its digits is 34020, while the sum is 36.

The square root of 639657 is about 799.7855962694. The cubic root of 639657 is about 86.1619896189.

It can be divided in two parts, 639 and 657, that added together give a 4-th power (1296 = 6⁴).

The spelling of 639657 in words is "six hundred thirty-nine thousand, six hundred fifty-seven".