855991 has 4 divisors (see below), whose sum is σ = 893232. Its totient is φ = 818752.

The previous prime is 855989. The next prime is 855997. The reversal of 855991 is 199558.

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 855991 - 2¹ = 855989 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 855991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (855997) 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 3 ways as a sum of consecutive naturals, for example, 18586 + ... + 18631.

It is an arithmetic number, because the mean of its divisors is an integer number (223308).

2⁸⁵⁵⁹⁹¹ is an apocalyptic number.

855991 is a deficient number, since it is larger than the sum of its proper divisors (37241).

855991 is a wasteful number, since it uses less digits than its factorization.

855991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37240.

The product of its digits is 16200, while the sum is 37.

The square root of 855991 is about 925.1978166857. The cubic root of 855991 is about 94.9488552035.

The spelling of 855991 in words is "eight hundred fifty-five thousand, nine hundred ninety-one".