21919 has 4 divisors (see below), whose sum is σ = 22896. Its totient is φ = 20944.

The previous prime is 21911. The next prime is 21929. The reversal of 21919 is 91912.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21919 - 2³ = 21911 is a prime.

It is a super-2 number, since 2×21919² = 960885122, which contains 22 as substring.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

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 21919.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21911) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 454 + ... + 499.

It is an arithmetic number, because the mean of its divisors is an integer number (5724).

2²¹⁹¹⁹ is an apocalyptic number.

21919 is a deficient number, since it is larger than the sum of its proper divisors (977).

21919 is an equidigital number, since it uses as much as digits as its factorization.

21919 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 976.

The product of its digits is 162, while the sum is 22.

The square root of 21919 is about 148.0506670029. The cubic root of 21919 is about 27.9859623512.

The spelling of 21919 in words is "twenty-one thousand, nine hundred nineteen".