644665 has 16 divisors (see below), whose sum is σ = 897408. Its totient is φ = 435456.

The previous prime is 644653. The next prime is 644669. The reversal of 644665 is 566446.

It is not a de Polignac number, because 644665 - 2⁹ = 644153 is a prime.

It is a Duffinian number.

Its product of digits (17280) is a multiple of the sum of its prime divisors (288).

It is not an unprimeable number, because it can be changed into a prime (644669) 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 15 ways as a sum of consecutive naturals, for example, 3874 + ... + 4036.

It is an arithmetic number, because the mean of its divisors is an integer number (56088).

2⁶⁴⁴⁶⁶⁵ is an apocalyptic number.

It is an amenable number.

644665 is a deficient number, since it is larger than the sum of its proper divisors (252743).

644665 is a wasteful number, since it uses less digits than its factorization.

644665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 288.

The product of its digits is 17280, while the sum is 31.

The square root of 644665 is about 802.9103312326. The cubic root of 644665 is about 86.3862650349.

The spelling of 644665 in words is "six hundred forty-four thousand, six hundred sixty-five".