644809 has 9 divisors (see below), whose sum is σ = 718599. Its totient is φ = 578160.

The previous prime is 644801. The next prime is 644837. The reversal of 644809 is 908446.

The square root of 644809 is 803.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 366025 + 278784 = 605^2 + 528^2 .

It is not a de Polignac number, because 644809 - 2³ = 644801 is a prime.

It is a Duffinian number.

644809 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (644801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 8797 + ... + 8869.

2⁶⁴⁴⁸⁰⁹ is an apocalyptic number.

644809 is the 803-rd square number.

644809 is the 402-nd centered octagonal number.

It is an amenable number.

644809 is a deficient number, since it is larger than the sum of its proper divisors (73790).

644809 is an equidigital number, since it uses as much as digits as its factorization.

644809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 168 (or 84 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 31.

The cubic root of 644809 is about 86.3926966420.

The spelling of 644809 in words is "six hundred forty-four thousand, eight hundred nine".