856821 has 8 divisors (see below), whose sum is σ = 1305664. Its totient is φ = 489600.

The previous prime is 856813. The next prime is 856831. The reversal of 856821 is 128658.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 856821 - 2³ = 856813 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 (856811) 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 7 ways as a sum of consecutive naturals, for example, 20380 + ... + 20421.

It is an arithmetic number, because the mean of its divisors is an integer number (163208).

2⁸⁵⁶⁸²¹ is an apocalyptic number.

It is an amenable number.

856821 is a deficient number, since it is larger than the sum of its proper divisors (448843).

856821 is a wasteful number, since it uses less digits than its factorization.

856821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40811.

The product of its digits is 3840, while the sum is 30.

The square root of 856821 is about 925.6462607281. The cubic root of 856821 is about 94.9795339107.

The spelling of 856821 in words is "eight hundred fifty-six thousand, eight hundred twenty-one".