21807 has 6 divisors (see below), whose sum is σ = 31512. Its totient is φ = 14532.

The previous prime is 21803. The next prime is 21817. The reversal of 21807 is 70812.

It is not a de Polignac number, because 21807 - 2² = 21803 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21807.

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 21807.

It is not an unprimeable number, because it can be changed into a prime (21803) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1203 + ... + 1220.

It is an arithmetic number, because the mean of its divisors is an integer number (5252).

2²¹⁸⁰⁷ is an apocalyptic number.

21807 is a deficient number, since it is larger than the sum of its proper divisors (9705).

21807 is a wasteful number, since it uses less digits than its factorization.

21807 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2429 (or 2426 counting only the distinct ones).

The product of its (nonzero) digits is 112, while the sum is 18.

The square root of 21807 is about 147.6719336909. The cubic root of 21807 is about 27.9382141012.

It can be divided in two parts, 2180 and 7, that added together give a 7-th power (2187 = 3⁷).

The spelling of 21807 in words is "twenty-one thousand, eight hundred seven".