21924 has 48 divisors (see below), whose sum is σ = 67200. Its totient is φ = 6048.

The previous prime is 21911. The next prime is 21929. The reversal of 21924 is 42912.

21924 = T₇₀ + T₇₁ + ... + T₇₇.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 21897 and 21906.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21929) by changing a digit.

21924 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 15 ways as a sum of consecutive naturals, for example, 742 + ... + 770.

It is an arithmetic number, because the mean of its divisors is an integer number (1400).

2²¹⁹²⁴ 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 21924, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33600).

21924 is an abundant number, since it is smaller than the sum of its proper divisors (45276).

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

21924 is a wasteful number, since it uses less digits than its factorization.

21924 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49 (or 41 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 21924 is about 148.0675521510. The cubic root of 21924 is about 27.9880901730.

It can be divided in two parts, 219 and 24, that added together give a 5-th power (243 = 3⁵).

The spelling of 21924 in words is "twenty-one thousand, nine hundred twenty-four".