21868 has 24 divisors (see below), whose sum is σ = 48384. Its totient is φ = 8400.

The previous prime is 21863. The next prime is 21871. The reversal of 21868 is 86812.

It is an Ulam number.

It is a plaindrome in base 16.

It is a zygodrome in base 5.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21863) by changing a digit.

21868 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 273 + ... + 343.

It is an arithmetic number, because the mean of its divisors is an integer number (2016).

2²¹⁸⁶⁸ is an apocalyptic number.

21868 is a gapful number since it is divisible by the number (28) 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 21868, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24192).

21868 is an abundant number, since it is smaller than the sum of its proper divisors (26516).

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

21868 is a wasteful number, since it uses less digits than its factorization.

21868 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 93 (or 91 counting only the distinct ones).

The product of its digits is 768, while the sum is 25.

The square root of 21868 is about 147.8783283649. The cubic root of 21868 is about 27.9642400633.

The spelling of 21868 in words is "twenty-one thousand, eight hundred sixty-eight".