22821 has 4 divisors (see below), whose sum is σ = 30432. Its totient is φ = 15212.

The previous prime is 22817. The next prime is 22853. The reversal of 22821 is 12822.

22821 is nontrivially palindromic in base 8.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 22821 - 2² = 22817 is a prime.

It is a D-number.

It is a plaindrome in base 12.

It is a self number, because there is not a number n which added to its sum of digits gives 22821.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (22811) 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 3 ways as a sum of consecutive naturals, for example, 3801 + ... + 3806.

It is an arithmetic number, because the mean of its divisors is an integer number (7608).

2²²⁸²¹ is an apocalyptic number.

It is an amenable number.

22821 is a deficient number, since it is larger than the sum of its proper divisors (7611).

22821 is an equidigital number, since it uses as much as digits as its factorization.

22821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7610.

The product of its digits is 64, while the sum is 15.

The square root of 22821 is about 151.0662106495. The cubic root of 22821 is about 28.3647018980.

Subtracting from 22821 its reverse (12822), we obtain a palindrome (9999).

The spelling of 22821 in words is "twenty-two thousand, eight hundred twenty-one".