686991 has 16 divisors (see below), whose sum is σ = 967680. Its totient is φ = 432960.

The previous prime is 686989. The next prime is 686993. The reversal of 686991 is 199686.

It is an interprime number because it is at equal distance from previous prime (686989) and next prime (686993).

It is not a de Polignac number, because 686991 - 2¹ = 686989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (686993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7675 + ... + 7763.

It is an arithmetic number, because the mean of its divisors is an integer number (60480).

2⁶⁸⁶⁹⁹¹ is an apocalyptic number.

686991 is a deficient number, since it is larger than the sum of its proper divisors (280689).

686991 is a wasteful number, since it uses less digits than its factorization.

686991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 206.

The product of its digits is 23328, while the sum is 39.

The square root of 686991 is about 828.8492022075. The cubic root of 686991 is about 88.2369218262.

The spelling of 686991 in words is "six hundred eighty-six thousand, nine hundred ninety-one".