686 has 8 divisors (see below), whose sum is σ = 1200. Its totient is φ = 294.

The previous prime is 683. The next prime is 691.

686 is nontrivially palindromic in base 10.

686 is an undulating number in base 10.

Its product of digits (288) is a multiple of the sum of its prime divisors (9).

It is a Curzon number.

It is a plaindrome in base 8 and base 16.

It is a nialpdrome in base 7 and base 9.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (683) 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, 95 + ... + 101.

It is an arithmetic number, because the mean of its divisors is an integer number (150).

2⁶⁸⁶ is an apocalyptic number.

686 is a deficient number, since it is larger than the sum of its proper divisors (514).

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

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

The sum of its prime factors is 23 (or 9 counting only the distinct ones).

The product of its digits is 288, while the sum is 20.

The square root of 686 is about 26.1916017074. The cubic root of 686 is about 8.8194473493.

Subtracting from 686 its sum of digits (20), we obtain a palindrome (666).

The spelling of 686 in words is "six hundred eighty-six", and thus it is an aban number and an oban number.