644325721 has 8 divisors (see below), whose sum is σ = 734706504. Its totient is φ = 559776000.

The previous prime is 644325709. The next prime is 644325751. The reversal of 644325721 is 127523446.

644325721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 4 ways, for example, as 228614400 + 415711321 = 15120^2 + 20389^2 .

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

It is not a de Polignac number, because 644325721 - 2¹³ = 644317529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644325751) 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, 1457530 + ... + 1457971.

It is an arithmetic number, because the mean of its divisors is an integer number (91838313).

Almost surely, 2^644325721 is an apocalyptic number.

It is an amenable number.

644325721 is a deficient number, since it is larger than the sum of its proper divisors (90380783).

644325721 is a wasteful number, since it uses less digits than its factorization.

644325721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2915531.

The product of its digits is 40320, while the sum is 34.

The square root of 644325721 is about 25383.5718723745. The cubic root of 644325721 is about 863.7110771092.

The spelling of 644325721 in words is "six hundred forty-four million, three hundred twenty-five thousand, seven hundred twenty-one".