639139720 has 64 divisors (see below), whose sum is σ = 1479928320. Its totient is φ = 248312064.

The previous prime is 639139691. The next prime is 639139723. The reversal of 639139720 is 27931936.

639139720 is digitally balanced in base 6, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (40).

It is not an unprimeable number, because it can be changed into a prime (639139723) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 216897 + ... + 219823.

It is an arithmetic number, because the mean of its divisors is an integer number (23123880).

Almost surely, 2^639139720 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 639139720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (739964160).

639139720 is an abundant number, since it is smaller than the sum of its proper divisors (840788600).

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

639139720 is a wasteful number, since it uses less digits than its factorization.

639139720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3094 (or 3090 counting only the distinct ones).

The product of its (nonzero) digits is 61236, while the sum is 40.

The square root of 639139720 is about 25281.2127873645. The cubic root of 639139720 is about 861.3875743164.

The spelling of 639139720 in words is "six hundred thirty-nine million, one hundred thirty-nine thousand, seven hundred twenty".