21823 has 4 divisors (see below), whose sum is σ = 22120. Its totient is φ = 21528.

The previous prime is 21821. The next prime is 21839. The reversal of 21823 is 32812.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21823 - 2¹ = 21821 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21797 and 21806.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21821) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 61 + ... + 217.

It is an arithmetic number, because the mean of its divisors is an integer number (5530).

2²¹⁸²³ is an apocalyptic number.

21823 is a deficient number, since it is larger than the sum of its proper divisors (297).

21823 is a wasteful number, since it uses less digits than its factorization.

21823 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 296.

The product of its digits is 96, while the sum is 16.

The square root of 21823 is about 147.7260978974. The cubic root of 21823 is about 27.9450452739.

The spelling of 21823 in words is "twenty-one thousand, eight hundred twenty-three".