686391 has 4 divisors (see below), whose sum is σ = 915192. Its totient is φ = 457592.

The previous prime is 686363. The next prime is 686417. The reversal of 686391 is 193686.

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 686391 - 2⁵ = 686359 is a prime.

It is a super-2 number, since 2×686391² = 942265209762, which contains 22 as substring.

It is an Ulam number.

It is a D-number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (686321) 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, 114396 + ... + 114401.

It is an arithmetic number, because the mean of its divisors is an integer number (228798).

2⁶⁸⁶³⁹¹ is an apocalyptic number.

686391 is a deficient number, since it is larger than the sum of its proper divisors (228801).

686391 is a wasteful number, since it uses less digits than its factorization.

686391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 228800.

The product of its digits is 7776, while the sum is 33.

The square root of 686391 is about 828.4871755193. The cubic root of 686391 is about 88.2112264030.

The spelling of 686391 in words is "six hundred eighty-six thousand, three hundred ninety-one".