644006 has 16 divisors (see below), whose sum is σ = 1070928. Its totient is φ = 288000.

The previous prime is 643991. The next prime is 644009. The reversal of 644006 is 600446.

It is a Curzon number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644006.

It is not an unprimeable number, because it can be changed into a prime (644009) by changing a digit.

644006 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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, 1406 + ... + 1806.

It is an arithmetic number, because the mean of its divisors is an integer number (66933).

2⁶⁴⁴⁰⁰⁶ is an apocalyptic number.

It is a pronic number, being equal to 802×803.

644006 is a deficient number, since it is larger than the sum of its proper divisors (426922).

644006 is a wasteful number, since it uses less digits than its factorization.

644006 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 487.

The product of its (nonzero) digits is 576, while the sum is 20.

The square root of 644006 is about 802.4998442367. The cubic root of 644006 is about 86.3568192722.

The spelling of 644006 in words is "six hundred forty-four thousand, six".