688639640 has 64 divisors (see below), whose sum is σ = 1676203200. Its totient is φ = 253112832.

The previous prime is 688639639. The next prime is 688639657. The reversal of 688639640 is 46936886.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 116189 + ... + 121971.

It is an arithmetic number, because the mean of its divisors is an integer number (26190675).

Almost surely, 2^688639640 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 688639640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (838101600).

688639640 is an abundant number, since it is smaller than the sum of its proper divisors (987563560).

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

688639640 is a wasteful number, since it uses less digits than its factorization.

688639640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6036 (or 6032 counting only the distinct ones).

The product of its (nonzero) digits is 1492992, while the sum is 50.

The square root of 688639640 is about 26241.9442877238. The cubic root of 688639640 is about 883.0744905130.

The spelling of 688639640 in words is "six hundred eighty-eight million, six hundred thirty-nine thousand, six hundred forty".