21984 has 24 divisors (see below), whose sum is σ = 57960. Its totient is φ = 7296.

The previous prime is 21977. The next prime is 21991. The reversal of 21984 is 48912.

It is an interprime number because it is at equal distance from previous prime (21977) and next prime (21991).

It is a tau number, because it is divible by the number of its divisors (24).

It is a Harshad number since it is a multiple of its sum of digits (24).

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 21984.

It is an unprimeable 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 3 ways as a sum of consecutive naturals, for example, 19 + ... + 210.

It is an arithmetic number, because the mean of its divisors is an integer number (2415).

2²¹⁹⁸⁴ is an apocalyptic number.

21984 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28980).

21984 is an abundant number, since it is smaller than the sum of its proper divisors (35976).

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

21984 is a wasteful number, since it uses less digits than its factorization.

21984 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 242 (or 234 counting only the distinct ones).

The product of its digits is 576, while the sum is 24.

The square root of 21984 is about 148.2700239428. The cubic root of 21984 is about 28.0135988365.

It can be divided in two parts, 219 and 84, that added together give a palindrome (303).

The spelling of 21984 in words is "twenty-one thousand, nine hundred eighty-four".