644730557 has 4 divisors (see below), whose sum is σ = 644804160. Its totient is φ = 644656956.

The previous prime is 644730551. The next prime is 644730577. The reversal of 644730557 is 755037446.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644730557 is a prime.

It is a super-2 number, since 2×644730557² = 831354982259060498, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644730551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21557 + ... + 41882.

It is an arithmetic number, because the mean of its divisors is an integer number (161201040).

Almost surely, 2^644730557 is an apocalyptic number.

It is an amenable number.

644730557 is a deficient number, since it is larger than the sum of its proper divisors (73603).

644730557 is a wasteful number, since it uses less digits than its factorization.

644730557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 73602.

The product of its (nonzero) digits is 352800, while the sum is 41.

The square root of 644730557 is about 25391.5449904097. The cubic root of 644730557 is about 863.8919318746.

The spelling of 644730557 in words is "six hundred forty-four million, seven hundred thirty thousand, five hundred fifty-seven".