21864 has 16 divisors (see below), whose sum is σ = 54720.
Its totient is φ = 7280.
The previous prime is 21863. The next prime is 21871. The reversal of 21864 is 46812.
It can be divided in two parts, 218 and 64, that added together give a palindrome (282).
It is a nude number because it is divisible by every one of its digits.
It is one of the 548 Lynch-Bell numbers.
It is a plaindrome in base 16.
It is a self number, because there is not a number n which added to its sum of digits gives 21864.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (21863) 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, 432 + ... + 479.
It is an arithmetic number, because the mean of its divisors is an integer number (3420).
221864 is an apocalyptic number.
21864 is a gapful number since it is divisible by the number (24) formed by its first and last digit.
It is an amenable number.
21864 is an abundant number, since it is smaller than the sum of its proper divisors (32856).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27360).
21864 is a wasteful number, since it uses less digits than its factorization.
21864 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 920 (or 916 counting only the distinct ones).
The product of its digits is 384, while the sum is 21.
The square root of 21864 is about 147.8648031142.
The cubic root of 21864 is about 27.9625349267.
The spelling of 21864 in words is "twenty-one thousand, eight hundred sixty-four".