20856 has 32 divisors (see below), whose sum is σ = 57600. Its totient is φ = 6240.

The previous prime is 20849. The next prime is 20857. The reversal of 20856 is 65802.

20856 = T₅₆ + T₅₇ + ... + T₆₆.

It is a happy number.

It is a nialpdrome in base 13.

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 20856.

It is not an unprimeable number, because it can be changed into a prime (20857) by changing a digit.

20856 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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, 225 + ... + 303.

It is an arithmetic number, because the mean of its divisors is an integer number (1800).

2²⁰⁸⁵⁶ 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 20856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28800).

20856 is an abundant number, since it is smaller than the sum of its proper divisors (36744).

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

20856 is a wasteful number, since it uses less digits than its factorization.

20856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 99 (or 95 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 20856 is about 144.4160655883. The cubic root of 20856 is about 27.5260359484.

The spelling of 20856 in words is "twenty thousand, eight hundred fifty-six".