639918756 has 72 divisors (see below), whose sum is σ = 1686484800. Its totient is φ = 204335040.

The previous prime is 639918703. The next prime is 639918757. The reversal of 639918756 is 657819936.

It is not an unprimeable number, because it can be changed into a prime (639918757) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 134425 + ... + 139103.

It is an arithmetic number, because the mean of its divisors is an integer number (23423400).

Almost surely, 2^639918756 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 639918756, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (843242400).

639918756 is an abundant number, since it is smaller than the sum of its proper divisors (1046566044).

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

639918756 is a wasteful number, since it uses less digits than its factorization.

639918756 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4849 (or 4844 counting only the distinct ones).

The product of its digits is 2449440, while the sum is 54.

The square root of 639918756 is about 25296.6155048457. The cubic root of 639918756 is about 861.7374088671.

The spelling of 639918756 in words is "six hundred thirty-nine million, nine hundred eighteen thousand, seven hundred fifty-six".