639640 has 16 divisors (see below), whose sum is σ = 1439280. Its totient is φ = 255840.

The previous prime is 639637. The next prime is 639647. The reversal of 639640 is 46936.

It is a junction number, because it is equal to n+sod(n) for n = 639599 and 639608.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639647) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7956 + ... + 8035.

It is an arithmetic number, because the mean of its divisors is an integer number (89955).

2⁶³⁹⁶⁴⁰ is an apocalyptic number.

It is an amenable number.

639640 is an abundant number, since it is smaller than the sum of its proper divisors (799640).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

639640 is a wasteful number, since it uses less digits than its factorization.

639640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16002 (or 15998 counting only the distinct ones).

The product of its (nonzero) digits is 3888, while the sum is 28.

The square root of 639640 is about 799.7749683505. The cubic root of 639640 is about 86.1612263105.

Subtracting from 639640 its reverse (46936), we obtain a cube (592704 = 84³).

The spelling of 639640 in words is "six hundred thirty-nine thousand, six hundred forty".