644005 has 8 divisors (see below), whose sum is σ = 813600. Its totient is φ = 488016.

The previous prime is 643991. The next prime is 644009. The reversal of 644005 is 500446.

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 644005 - 2⁹ = 643493 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (19).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644009) 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 7 ways as a sum of consecutive naturals, for example, 3295 + ... + 3484.

It is an arithmetic number, because the mean of its divisors is an integer number (101700).

2⁶⁴⁴⁰⁰⁵ is an apocalyptic number.

It is an amenable number.

644005 is a deficient number, since it is larger than the sum of its proper divisors (169595).

644005 is a wasteful number, since it uses less digits than its factorization.

644005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6803.

The product of its (nonzero) digits is 480, while the sum is 19.

The square root of 644005 is about 802.4992211834. The cubic root of 644005 is about 86.3567745744.

The spelling of 644005 in words is "six hundred forty-four thousand, five".