639940 has 36 divisors (see below), whose sum is σ = 1565676. Its totient is φ = 219072.

The previous prime is 639937. The next prime is 639941. The reversal of 639940 is 49936.

It can be written as a sum of positive squares in 2 ways, for example, as 188356 + 451584 = 434^2 + 672^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639941) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 654 + ... + 1306.

It is an arithmetic number, because the mean of its divisors is an integer number (43491).

2⁶³⁹⁹⁴⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 639940, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (782838).

639940 is an abundant number, since it is smaller than the sum of its proper divisors (925736).

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

639940 is a wasteful number, since it uses less digits than its factorization.

639940 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 676 (or 667 counting only the distinct ones).

The product of its (nonzero) digits is 5832, while the sum is 31.

The square root of 639940 is about 799.9624991211. The cubic root of 639940 is about 86.1746944738.

The spelling of 639940 in words is "six hundred thirty-nine thousand, nine hundred forty".