643809 has 4 divisors (see below), whose sum is σ = 858416. Its totient is φ = 429204.

The previous prime is 643781. The next prime is 643847. The reversal of 643809 is 908346.

643809 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 not a de Polignac number, because 643809 - 2⁷ = 643681 is a prime.

It is a D-number.

It is a Duffinian number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 643809.

It is not an unprimeable number, because it can be changed into a prime (643849) 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, 107299 + ... + 107304.

It is an arithmetic number, because the mean of its divisors is an integer number (214604).

2⁶⁴³⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

643809 is a deficient number, since it is larger than the sum of its proper divisors (214607).

643809 is a wasteful number, since it uses less digits than its factorization.

643809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 214606.

The product of its (nonzero) digits is 5184, while the sum is 30.

The square root of 643809 is about 802.3770933919. The cubic root of 643809 is about 86.3480129213.

The spelling of 643809 in words is "six hundred forty-three thousand, eight hundred nine".