857991 has 4 divisors (see below), whose sum is σ = 1143992. Its totient is φ = 571992.

The previous prime is 857981. The next prime is 858001. The reversal of 857991 is 199758.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (857981) and next prime (858001).

It is not a de Polignac number, because 857991 - 2⁵ = 857959 is a prime.

It is a super-2 number, since 2×857991² = 1472297112162, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (857951) 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 3 ways as a sum of consecutive naturals, for example, 142996 + ... + 143001.

It is an arithmetic number, because the mean of its divisors is an integer number (285998).

2⁸⁵⁷⁹⁹¹ is an apocalyptic number.

857991 is a deficient number, since it is larger than the sum of its proper divisors (286001).

857991 is a wasteful number, since it uses less digits than its factorization.

857991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 286000.

The product of its digits is 22680, while the sum is 39.

The square root of 857991 is about 926.2780360129. The cubic root of 857991 is about 95.0227461693.

The spelling of 857991 in words is "eight hundred fifty-seven thousand, nine hundred ninety-one".