644007 has 24 divisors (see below), whose sum is σ = 1078896. Its totient is φ = 338688.

The previous prime is 643991. The next prime is 644009. The reversal of 644007 is 700446.

It is not a de Polignac number, because 644007 - 2⁴ = 643991 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is the 803-rd Hogben number.

644007 is a lucky number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644007.

It is not an unprimeable number, because it can be changed into a prime (644009) by changing a digit.

It is a nontrivial repunit in base 802.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1743 + ... + 2079.

It is an arithmetic number, because the mean of its divisors is an integer number (44954).

2⁶⁴⁴⁰⁰⁷ is an apocalyptic number.

644007 is a deficient number, since it is larger than the sum of its proper divisors (434889).

644007 is a wasteful number, since it uses less digits than its factorization.

644007 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 367 (or 360 counting only the distinct ones).

The product of its (nonzero) digits is 672, while the sum is 21.

The square root of 644007 is about 802.5004672896. The cubic root of 644007 is about 86.3568639699.

The spelling of 644007 in words is "six hundred forty-four thousand, seven".