686691 has 16 divisors (see below), whose sum is σ = 1053600. Its totient is φ = 441504.

The previous prime is 686687. The next prime is 686723. The reversal of 686691 is 196686.

It is not a de Polignac number, because 686691 - 2² = 686687 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

686691 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (686611) 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 15 ways as a sum of consecutive naturals, for example, 345 + ... + 1221.

It is an arithmetic number, because the mean of its divisors is an integer number (65850).

2⁶⁸⁶⁶⁹¹ is an apocalyptic number.

686691 is a deficient number, since it is larger than the sum of its proper divisors (366909).

686691 is a wasteful number, since it uses less digits than its factorization.

686691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 915 (or 909 counting only the distinct ones).

The product of its digits is 15552, while the sum is 36.

The square root of 686691 is about 828.6682086336. The cubic root of 686691 is about 88.2240759856.

The spelling of 686691 in words is "six hundred eighty-six thousand, six hundred ninety-one".