644685 has 8 divisors (see below), whose sum is σ = 1031520. Its totient is φ = 343824.

The previous prime is 644671. The next prime is 644687. The reversal of 644685 is 586446.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 644685 - 2⁴ = 644669 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644687) 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, 21475 + ... + 21504.

It is an arithmetic number, because the mean of its divisors is an integer number (128940).

2⁶⁴⁴⁶⁸⁵ is an apocalyptic number.

It is an amenable number.

644685 is a deficient number, since it is larger than the sum of its proper divisors (386835).

644685 is a wasteful number, since it uses less digits than its factorization.

644685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42987.

The product of its digits is 23040, while the sum is 33.

The square root of 644685 is about 802.9227858269. The cubic root of 644685 is about 86.3871583709.

The spelling of 644685 in words is "six hundred forty-four thousand, six hundred eighty-five".