639979940 has 24 divisors (see below), whose sum is σ = 1345388352. Its totient is φ = 255719520.

The previous prime is 639979939. The next prime is 639979957. The reversal of 639979940 is 49979936.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2795 + ... + 35885.

It is an arithmetic number, because the mean of its divisors is an integer number (56057848).

Almost surely, 2^639979940 is an apocalyptic number.

It is an amenable number.

639979940 is an abundant number, since it is smaller than the sum of its proper divisors (705408412).

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

639979940 is a wasteful number, since it uses less digits than its factorization.

639979940 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34067 (or 34065 counting only the distinct ones).

The product of its (nonzero) digits is 3306744, while the sum is 56.

The square root of 639979940 is about 25297.8248076786. The cubic root of 639979940 is about 861.7648721770.

It can be divided in two parts, 63997 and 9940, that added together give a palindrome (73937).

The spelling of 639979940 in words is "six hundred thirty-nine million, nine hundred seventy-nine thousand, nine hundred forty".