821856 has 48 divisors (see below), whose sum is σ = 2467584. Its totient is φ = 234624.

The previous prime is 821851. The next prime is 821857. The reversal of 821856 is 658128.

821856 = T₁₂₉ + T₁₃₀ + ... + T₁₉₁.

It is a tau number, because it is divible by the number of its divisors (48).

It is an Ulam number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 821856.

It is not an unprimeable number, because it can be changed into a prime (821851) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 61 + ... + 1283.

It is an arithmetic number, because the mean of its divisors is an integer number (51408).

2⁸²¹⁸⁵⁶ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 821856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1233792).

821856 is an abundant number, since it is smaller than the sum of its proper divisors (1645728).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

821856 is a wasteful number, since it uses less digits than its factorization.

821856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1243 (or 1235 counting only the distinct ones).

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

The square root of 821856 is about 906.5627391416. The cubic root of 821856 is about 93.6695808136.

The spelling of 821856 in words is "eight hundred twenty-one thousand, eight hundred fifty-six".