644868 has 48 divisors (see below), whose sum is σ = 1912960. Its totient is φ = 184032.

The previous prime is 644867. The next prime is 644869. The reversal of 644868 is 868446.

644868 is a `hidden beast` number, since 644 + 8 + 6 + 8 = 666.

It is an interprime number because it is at equal distance from previous prime (644867) and next prime (644869).

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (644863) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 330 + ... + 1182.

2⁶⁴⁴⁸⁶⁸ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644868, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (956480).

644868 is an abundant number, since it is smaller than the sum of its proper divisors (1268092).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644868 is a wasteful number, since it uses less digits than its factorization.

644868 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 873 (or 865 counting only the distinct ones).

The product of its digits is 36864, while the sum is 36.

The square root of 644868 is about 803.0367363950. The cubic root of 644868 is about 86.3953315379.

The spelling of 644868 in words is "six hundred forty-four thousand, eight hundred sixty-eight".