644043857 has 4 divisors (see below), whose sum is σ = 645039936. Its totient is φ = 643047780.

The previous prime is 644043791. The next prime is 644043871. The reversal of 644043857 is 758340446.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 644043857 - 2⁸ = 644043601 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644043877) 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 3 ways as a sum of consecutive naturals, for example, 497069 + ... + 498362.

It is an arithmetic number, because the mean of its divisors is an integer number (161259984).

Almost surely, 2^644043857 is an apocalyptic number.

It is an amenable number.

644043857 is a deficient number, since it is larger than the sum of its proper divisors (996079).

644043857 is an equidigital number, since it uses as much as digits as its factorization.

644043857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 996078.

The product of its (nonzero) digits is 322560, while the sum is 41.

The square root of 644043857 is about 25378.0191701401. The cubic root of 644043857 is about 863.5851136102.

The spelling of 644043857 in words is "six hundred forty-four million, forty-three thousand, eight hundred fifty-seven".