644755 has 4 divisors (see below), whose sum is σ = 773712. Its totient is φ = 515800.

The previous prime is 644753. The next prime is 644767. The reversal of 644755 is 557446.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 644755 - 2¹ = 644753 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644753) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64471 + ... + 64480.

It is an arithmetic number, because the mean of its divisors is an integer number (193428).

2⁶⁴⁴⁷⁵⁵ is an apocalyptic number.

644755 is a deficient number, since it is larger than the sum of its proper divisors (128957).

644755 is a wasteful number, since it uses less digits than its factorization.

644755 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128956.

The product of its digits is 16800, while the sum is 31.

The square root of 644755 is about 802.9663753857. The cubic root of 644755 is about 86.3902849016.

The spelling of 644755 in words is "six hundred forty-four thousand, seven hundred fifty-five".