644666 has 8 divisors (see below), whose sum is σ = 1054944. Its totient is φ = 293020.

The previous prime is 644653. The next prime is 644669. The reversal of 644666 is 666446.

It is a happy number.

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

644666 is a modest number, since divided by 666 gives 644 as remainder.

It is a Curzon number.

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 3 ways as a sum of consecutive naturals, for example, 14630 + ... + 14673.

It is an arithmetic number, because the mean of its divisors is an integer number (131868).

2⁶⁴⁴⁶⁶⁶ is an apocalyptic number.

644666 is a deficient number, since it is larger than the sum of its proper divisors (410278).

644666 is a wasteful number, since it uses less digits than its factorization.

644666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29316.

The product of its digits is 20736, while the sum is 32.

The square root of 644666 is about 802.9109539669. The cubic root of 644666 is about 86.3863097021.

The spelling of 644666 in words is "six hundred forty-four thousand, six hundred sixty-six".