21726 has 24 divisors (see below), whose sum is σ = 50544. Its totient is φ = 6720.

The previous prime is 21713. The next prime is 21727. The reversal of 21726 is 62712.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21699 and 21708.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21727) by changing a digit.

21726 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 11 ways as a sum of consecutive naturals, for example, 271 + ... + 341.

It is an arithmetic number, because the mean of its divisors is an integer number (2106).

2²¹⁷²⁶ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21726, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25272).

21726 is an abundant number, since it is smaller than the sum of its proper divisors (28818).

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

21726 is a wasteful number, since it uses less digits than its factorization.

21726 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 96 (or 93 counting only the distinct ones).

The product of its digits is 168, while the sum is 18.

The square root of 21726 is about 147.3974219585. The cubic root of 21726 is about 27.9035799160.

It can be divided in two parts, 217 and 26, that added together give a 5-th power (243 = 3⁵).

The spelling of 21726 in words is "twenty-one thousand, seven hundred twenty-six".