685891 has 4 divisors (see below), whose sum is σ = 692784. Its totient is φ = 679000.

The previous prime is 685859. The next prime is 685907. The reversal of 685891 is 198586.

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

It is a cyclic number.

It is not a de Polignac number, because 685891 - 2⁵ = 685859 is a prime.

It is a Duffinian number.

685891 is a lucky number.

It is a nialpdrome in base 16.

It is a self number, because there is not a number n which added to its sum of digits gives 685891.

It is not an unprimeable number, because it can be changed into a prime (685591) 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 3 ways as a sum of consecutive naturals, for example, 3295 + ... + 3496.

It is an arithmetic number, because the mean of its divisors is an integer number (173196).

2⁶⁸⁵⁸⁹¹ is an apocalyptic number.

685891 is a deficient number, since it is larger than the sum of its proper divisors (6893).

685891 is a wasteful number, since it uses less digits than its factorization.

685891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6892.

The product of its digits is 17280, while the sum is 37.

The square root of 685891 is about 828.1853657244. The cubic root of 685891 is about 88.1898021094.

The spelling of 685891 in words is "six hundred eighty-five thousand, eight hundred ninety-one".