685809 has 12 divisors (see below), whose sum is σ = 998452. Its totient is φ = 453600.

The previous prime is 685793. The next prime is 685819. The reversal of 685809 is 908586.

It can be written as a sum of positive squares in 2 ways, for example, as 5184 + 680625 = 72^2 + 825^2 .

It is not a de Polignac number, because 685809 - 2⁴ = 685793 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (685819) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1419 + ... + 1839.

2⁶⁸⁵⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

685809 is a deficient number, since it is larger than the sum of its proper divisors (312643).

685809 is a wasteful number, since it uses less digits than its factorization.

685809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 608 (or 605 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 36.

The square root of 685809 is about 828.1358584194. The cubic root of 685809 is about 88.1862875315.

The spelling of 685809 in words is "six hundred eighty-five thousand, eight hundred nine".