686809 has 4 divisors (see below), whose sum is σ = 693220. Its totient is φ = 680400.

The previous prime is 686801. The next prime is 686837. The reversal of 686809 is 908686.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 451584 + 235225 = 672^2 + 485^2 .

It is a cyclic number.

It is not a de Polignac number, because 686809 - 2³ = 686801 is a prime.

It is a Duffinian number.

686809 is a lucky number.

It is a nialpdrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (686801) 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, 3042 + ... + 3259.

It is an arithmetic number, because the mean of its divisors is an integer number (173305).

2⁶⁸⁶⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

686809 is a deficient number, since it is larger than the sum of its proper divisors (6411).

686809 is a wasteful number, since it uses less digits than its factorization.

686809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6410.

The product of its (nonzero) digits is 20736, while the sum is 37.

The square root of 686809 is about 828.7394041555. The cubic root of 686809 is about 88.2291291292.

The spelling of 686809 in words is "six hundred eighty-six thousand, eight hundred nine".