644700721 has 8 divisors (see below), whose sum is σ = 737321600. Its totient is φ = 552210048.

The previous prime is 644700713. The next prime is 644700731. The reversal of 644700721 is 127007446.

644700721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 644700721 - 2³ = 644700713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644700701) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21696 + ... + 41953.

It is an arithmetic number, because the mean of its divisors is an integer number (92165200).

Almost surely, 2^644700721 is an apocalyptic number.

It is an amenable number.

644700721 is a deficient number, since it is larger than the sum of its proper divisors (92620879).

644700721 is a wasteful number, since it uses less digits than its factorization.

644700721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 65103.

The product of its (nonzero) digits is 9408, while the sum is 31.

The square root of 644700721 is about 25390.9574652080. The cubic root of 644700721 is about 863.8786056476.

The spelling of 644700721 in words is "six hundred forty-four million, seven hundred thousand, seven hundred twenty-one".