21719 has 4 divisors (see below), whose sum is σ = 22344. Its totient is φ = 21096.

The previous prime is 21713. The next prime is 21727. The reversal of 21719 is 91712.

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 21719 - 2¹² = 17623 is a prime.

It is a super-2 number, since 2×21719² = 943429922, which contains 22 as substring.

It is a Duffinian number.

It is a plaindrome in base 15.

It is a self number, because there is not a number n which added to its sum of digits gives 21719.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21713) 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, 257 + ... + 330.

It is an arithmetic number, because the mean of its divisors is an integer number (5586).

2²¹⁷¹⁹ is an apocalyptic number.

21719 is a deficient number, since it is larger than the sum of its proper divisors (625).

21719 is an equidigital number, since it uses as much as digits as its factorization.

21719 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 624.

The product of its digits is 126, while the sum is 20.

The square root of 21719 is about 147.3736747184. The cubic root of 21719 is about 27.9005827998.

The spelling of 21719 in words is "twenty-one thousand, seven hundred nineteen".