644653221 has 8 divisors (see below), whose sum is σ = 860403744. Its totient is φ = 429335760.

The previous prime is 644653213. The next prime is 644653237. The reversal of 644653221 is 122356446.

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

It is not a de Polignac number, because 644653221 - 2³ = 644653213 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644653211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 104775 + ... + 110756.

It is an arithmetic number, because the mean of its divisors is an integer number (107550468).

Almost surely, 2^644653221 is an apocalyptic number.

It is an amenable number.

644653221 is a deficient number, since it is larger than the sum of its proper divisors (215750523).

644653221 is a wasteful number, since it uses less digits than its factorization.

644653221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 216531.

The product of its digits is 34560, while the sum is 33.

The square root of 644653221 is about 25390.0220756107. The cubic root of 644653221 is about 863.8573889599.

The spelling of 644653221 in words is "six hundred forty-four million, six hundred fifty-three thousand, two hundred twenty-one".