639968640 has 256 divisors, whose sum is σ = 2194387200. Its totient is φ = 158146560.

The previous prime is 639968617. The next prime is 639968669. The reversal of 639968640 is 46869936.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1933275 + ... + 1933605.

It is an arithmetic number, because the mean of its divisors is an integer number (8571825).

Almost surely, 2^639968640 is an apocalyptic number.

639968640 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 639968640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1097193600).

639968640 is an abundant number, since it is smaller than the sum of its proper divisors (1554418560).

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

639968640 is a wasteful number, since it uses less digits than its factorization.

639968640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 425 (or 413 counting only the distinct ones).

The product of its (nonzero) digits is 1679616, while the sum is 51.

The square root of 639968640 is about 25297.6014673328. The cubic root of 639968640 is about 861.7598001429.

The spelling of 639968640 in words is "six hundred thirty-nine million, nine hundred sixty-eight thousand, six hundred forty".