856991 has 4 divisors (see below), whose sum is σ = 859872. Its totient is φ = 854112.

The previous prime is 856969. The next prime is 856993. The reversal of 856991 is 199658.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199658 = 2 ⋅99829.

It is a cyclic number.

It is not a de Polignac number, because 856991 - 2⁶ = 856927 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (856993) 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, 935 + ... + 1608.

It is an arithmetic number, because the mean of its divisors is an integer number (214968).

2⁸⁵⁶⁹⁹¹ is an apocalyptic number.

856991 is a deficient number, since it is larger than the sum of its proper divisors (2881).

856991 is a wasteful number, since it uses less digits than its factorization.

856991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2880.

The product of its digits is 19440, while the sum is 38.

The square root of 856991 is about 925.7380839093. The cubic root of 856991 is about 94.9858150566.

The spelling of 856991 in words is "eight hundred fifty-six thousand, nine hundred ninety-one".