644656 has 20 divisors (see below), whose sum is σ = 1279432. Its totient is φ = 314496.

The previous prime is 644653. The next prime is 644669. The reversal of 644656 is 656446.

It is not an unprimeable number, because it can be changed into a prime (644653) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 220 + ... + 1156.

2⁶⁴⁴⁶⁵⁶ is an apocalyptic number.

It is an amenable number.

644656 is a deficient number, since it is larger than the sum of its proper divisors (634776).

644656 is a wasteful number, since it uses less digits than its factorization.

644656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 988 (or 982 counting only the distinct ones).

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

The square root of 644656 is about 802.9047266021. The cubic root of 644656 is about 86.3858630277.

The spelling of 644656 in words is "six hundred forty-four thousand, six hundred fifty-six".