644768 has 12 divisors (see below), whose sum is σ = 1269450. Its totient is φ = 322368.

The previous prime is 644767. The next prime is 644783. The reversal of 644768 is 867446.

It can be written as a sum of positive squares in only one way, i.e., 559504 + 85264 = 748^2 + 292^2 .

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644768.

It is not an unprimeable number, because it can be changed into a prime (644767) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10043 + ... + 10106.

2⁶⁴⁴⁷⁶⁸ is an apocalyptic number.

It is an amenable number.

644768 is a deficient number, since it is larger than the sum of its proper divisors (624682).

644768 is a wasteful number, since it uses less digits than its factorization.

644768 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20159 (or 20151 counting only the distinct ones).

The product of its digits is 32256, while the sum is 35.

The square root of 644768 is about 802.9744703289. The cubic root of 644768 is about 86.3908655181.

The spelling of 644768 in words is "six hundred forty-four thousand, seven hundred sixty-eight".