643657728 has 156 divisors (see below), whose sum is σ = 1998276360. Its totient is φ = 183730176.

The previous prime is 643657711. The next prime is 643657733. The reversal of 643657728 is 827756346.

It is a Harshad number since it is a multiple of its sum of digits (48).

It is a congruent number.

It is an unprimeable number.

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 11 ways as a sum of consecutive naturals, for example, 601578 + ... + 602646.

Almost surely, 2^643657728 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 643657728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (999138180).

643657728 is an abundant number, since it is smaller than the sum of its proper divisors (1354618632).

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

643657728 is a wasteful number, since it uses less digits than its factorization.

643657728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1110 (or 1081 counting only the distinct ones).

The product of its digits is 1693440, while the sum is 48.

The square root of 643657728 is about 25370.4104815038. The cubic root of 643657728 is about 863.4124949732.

The spelling of 643657728 in words is "six hundred forty-three million, six hundred fifty-seven thousand, seven hundred twenty-eight".