644423257 has 8 divisors (see below), whose sum is σ = 666812160. Its totient is φ = 622134480.

The previous prime is 644423249. The next prime is 644423291. The reversal of 644423257 is 752324446.

644423257 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 644423257 - 2³ = 644423249 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644423357) 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, 11818 + ... + 37795.

It is an arithmetic number, because the mean of its divisors is an integer number (83351520).

Almost surely, 2^644423257 is an apocalyptic number.

It is an amenable number.

644423257 is a deficient number, since it is larger than the sum of its proper divisors (22388903).

644423257 is a wasteful number, since it uses less digits than its factorization.

644423257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50063.

The product of its digits is 161280, while the sum is 37.

The square root of 644423257 is about 25385.4930422870. The cubic root of 644423257 is about 863.7546568653.

It can be divided in two parts, 644423 and 257, that added together give a triangular number (644680 = T₁₁₃₅).

The spelling of 644423257 in words is "six hundred forty-four million, four hundred twenty-three thousand, two hundred fifty-seven".