6640921728 has 256 divisors, whose sum is σ = 22683168000. Its totient is φ = 1896846336.

The previous prime is 6640921717. The next prime is 6640921751. The reversal of 6640921728 is 8271290466.

It is a happy number.

6640921728 is a `hidden beast` number, since 6 + 6 + 409 + 217 + 28 = 666.

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, 1957858 + ... + 1961246.

It is an arithmetic number, because the mean of its divisors is an integer number (88606125).

Almost surely, 2^6640921728 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 6640921728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (11341584000).

6640921728 is an abundant number, since it is smaller than the sum of its proper divisors (16042246272).

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

6640921728 is an frugal number, since it uses more digits than its factorization.

6640921728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3431 (or 3401 counting only the distinct ones).

The product of its (nonzero) digits is 290304, while the sum is 45.

The square root of 6640921728 is about 81491.8506845930. The cubic root of 6640921728 is about 1879.6462409672.

The spelling of 6640921728 in words is "six billion, six hundred forty million, nine hundred twenty-one thousand, seven hundred twenty-eight".