644689 has 4 divisors (see below), whose sum is σ = 678640. Its totient is φ = 610740.

The previous prime is 644687. The next prime is 644701. The reversal of 644689 is 986446.

644689 = T₁₂₁ + T₁₂₂ + ... + T₁₇₇.

644689 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 644689 - 2¹ = 644687 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644687) 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, 16947 + ... + 16984.

It is an arithmetic number, because the mean of its divisors is an integer number (169660).

2⁶⁴⁴⁶⁸⁹ is an apocalyptic number.

It is an amenable number.

644689 is a deficient number, since it is larger than the sum of its proper divisors (33951).

644689 is a wasteful number, since it uses less digits than its factorization.

644689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33950.

The product of its digits is 41472, while the sum is 37.

The square root of 644689 is about 802.9252767226. The cubic root of 644689 is about 86.3873370359.

It can be divided in two parts, 64 and 4689, that added together give a triangular number (4753 = T₉₇).

The spelling of 644689 in words is "six hundred forty-four thousand, six hundred eighty-nine".